Reishi Mushrooms: Which Benefits Do They Really Have?

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The 10almonds Team

Reishi Mushrooms

Another Monday Research Review, another mushroom! If we keep this up, we’ll have to rename it “Mushroom Monday”.

But, there’s so much room for things to say, and these are fun guys to write about, as we check the science for any spore’ious claims…

Why do people take reishi?

Popular health claims for the reishi mushroom include:

  • Immune health
  • Cardiovascular health
  • Protection against cancer
  • Antioxidant qualities
  • Reduced fatigue and anxiety

And does the science agree?

Let’s take a look, claim by claim:

Immune health

A lot of research for this has been in vitro (ie, with cell cultures in labs), but promising, for example:

Immunomodulating Effect of Ganoderma lucidum (Lingzhi) and Possible Mechanism

(that is the botanical name for reishi, and the Chinese name for it, by the way)

That’s not to say there are no human studies though; here it was found to boost T-cell production in stressed athletes:

Effect of Ganoderma lucidum capsules on T lymphocyte subsets in football players on “living high-training low”

Cardiovascular health

Here we found a stack of evidence for statistically insignificant improvements in assorted measures of cardiovascular health, and some studies where reishi did not outperform placebo.

Because the studies were really not that compelling, instead of taking up room (and your time) with them, we’re going to move onto more compelling, exciting science, such as…

Protection against cancer

There’s a lot of high quality research for this, and a lot of good results. The body of evidence here is so large that even back as far as 2005, the question was no longer “does it work” or even “how does it work”, but rather “we need more clinical studies to find the best doses”. Researchers even added:

❝At present, lingzhi is a health food supplement to support cancer patients, yet the evidence supporting the potential of direct in vivo anticancer effects should not be underestimated.❞

~ Yuen et al.

Check it out:

Anticancer effects of Ganoderma lucidum: a review of scientific evidence

Just so you know we’re not kidding about the weight of evidence, let’s drop a few extra sources:

By the way, we shortened most of those titles for brevity, but almost all of the continued with “by” followed by a one-liner of how it does it.

So it’s not a “mysterious action” thing, it’s a “this is a very potent medicine and we know how it works” thing.

Antioxidant qualities

Here we literally only found studies to say no change was found, one that found a slight increase of antioxidant levels in urine. It’s worth noting that levels of a given thing (or its metabolites, in the case of some things) in urine are often quite unhelpful regards knowing what’s going on in the body, because we get to measure only what the body lost, not what it gained/kept.

So again, let’s press on:

Reduced fatigue and anxiety

Most of the studies for this that we could find pertained to health-related quality of life for cancer patients specifically, so (while they universally give glowing reports of reishi’s benefits to health and happiness of cancer patients), that’s a confounding factor when it comes to isolating its effects on reduction of fatigue and anxiety in people without cancer.

Here’s one that looked at it in the case of reduction of fatigue, anxiety, and other factors, in patients without cancer (but with neurathenia), in which they found it was “significantly superior to placebo with respect to the clinical improvement of symptoms”.

Summary:

  • Reishi mushroom’s anti-cancer properties are very, very clear
  • There is also good science to back immune health claims
  • It also has been found to significantly reduce fatigue and anxiety in unwell patients (we’d love to see more studies on its benefits in otherwise healthy people, though)

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  • Voluntary assisted dying is different to suicide. But federal laws conflate them and restrict access to telehealth

    Michaela Estelle Okninski – University of Adelaide; Marc Trabsky – La Trobe University; Neera Bhatia – Deakin University

    10almonds is reader-supported. We may, at no cost to you, receive a portion of sales if you purchase a product through a link in this article.

    Voluntary assisted dying is now lawful in every Australian state and will soon begin in the Australian Capital Territory.

    However, it’s illegal to discuss it via telehealth. That means people who live in rural and remote areas, or those who can’t physically go to see a doctor, may not be able to access the scheme.

    A federal private members bill, introduced to parliament last week, aims to change this. So what’s proposed and why is it needed?

    What’s wrong with the current laws?

    Voluntary assisted dying doesn’t meet the definition of suicide under state laws.

    But the Commonwealth Criminal Code prohibits the discussion or dissemination of suicide-related material electronically.

    This opens doctors to the risk of criminal prosecution if they discuss voluntary assisted dying via telehealth.

    Successive Commonwealth attorneys-general have failed to address the conflict between federal and state laws, despite persistent calls from state attorneys-general for necessary clarity.

    This eventually led to voluntary assistant dying doctor Nicholas Carr calling on the Federal Court of Australia to resolve this conflict. Carr sought a declaration to exclude voluntary assisted dying from the definition of suicide under the Criminal Code.

    In November, the court declared voluntary assisted dying was considered suicide for the purpose of the Criminal Code. This meant doctors across Australia were prohibited from using telehealth services for voluntary assisted dying consultations.

    Last week, independent federal MP Kate Chaney introduced a private members bill to create an exemption for voluntary assisted dying by excluding it as suicide for the purpose of the Criminal Code. Here’s why it’s needed.

    Not all patients can physically see a doctor

    Defining voluntary assisted dying as suicide in the Criminal Code disproportionately impacts people living in regional and remote areas. People in the country rely on the use of “carriage services”, such as phone and video consultations, to avoid travelling long distances to consult their doctor.

    Other people with terminal illnesses, whether in regional or urban areas, may be suffering intolerably and unable to physically attend appointments with doctors.

    The prohibition against telehealth goes against the principles of voluntary assisted dying, which are to minimise suffering, maximise quality of life and promote autonomy.

    Old hands hold young hands
    Some people aren’t able to attend doctors’ appointments in person.
    Jeffrey M Levine/Shutterstock

    Doctors don’t want to be involved in ‘suicide’

    Equating voluntary assisted dying with suicide has a direct impact on doctors, who fear criminal prosecution due to the prohibition against using telehealth.

    Some doctors may decide not to help patients who choose voluntary assisted dying, leaving patients in a state of limbo.

    The number of doctors actively participating in voluntary assisted dying is already low. The majority of doctors are located in metropolitan areas or major regional centres, leaving some locations with very few doctors participating in voluntary assisted dying.

    It misclassifies deaths

    In state law, people dying under voluntary assisted dying have the cause of their death registered as “the disease, illness or medical condition that was the grounds for a person to access voluntary assisted dying”, while the manner of dying is recorded as voluntary assisted dying.

    In contrast, only coroners in each state and territory can make a finding of suicide as a cause of death.

    In 2017, voluntary assisted dying was defined in the Coroners Act 2008 (Vic) as not a reportable death, and thus not suicide.

    The language of suicide is inappropriate for explaining how people make a decision to die with dignity under the lawful practice of voluntary assisted dying.

    There is ongoing taboo and stigma attached to suicide. People who opt for and are lawfully eligible to access voluntary assisted dying should not be tainted with the taboo that currently surrounds suicide.

    So what is the solution?

    The only way to remedy this problem is for the federal government to create an exemption in the Criminal Code to allow telehealth appointments to discuss voluntary assisted dying.

    Chaney’s private member’s bill is yet to be debated in federal parliament.

    If it’s unsuccessful, the Commonwealth attorney-general should pass regulations to exempt voluntary assisted dying as suicide.

    A cooperative approach to resolve this conflict of laws is necessary to ensure doctors don’t risk prosecution for assisting eligible people to access voluntary assisted dying, regional and remote patients have access to voluntary assisted dying, families don’t suffer consequences for the erroneous classification of voluntary assisted dying as suicide, and people accessing voluntary assisted dying are not shrouded with the taboo of suicide when accessing a lawful practice to die with dignity.

    Failure to change this will cause unnecessary suffering for patients and doctors alike.The Conversation

    Michaela Estelle Okninski, Lecturer of Law, University of Adelaide; Marc Trabsky, Associate professor, La Trobe University, and Neera Bhatia, Associate Professor in Law, Deakin University

    This article is republished from The Conversation under a Creative Commons license. Read the original article.

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  • Psychology Sunday: Family Estrangment & How To Fix It

    The 10almonds Team

    10almonds is reader-supported. We may, at no cost to you, receive a portion of sales if you purchase a product through a link in this article.

    Estrangement, And How To Heal It

    We’ve written before about how deleterious to the health loneliness and isolation can be, and what things can be done about it. Today, we’re tackling a related but different topic.

    We recently had a request to write about…

    ❝Reconciliation of relationships in particular estrangement mother adult daughter❞

    And, this is not only an interesting topic, but a very specific one that affects more people than is commonly realized!

    In fact, a recent 800-person study found that more than 43% of people experienced family estrangement of one sort or another, and a more specific study of more than 2,000 mother-child pairs found that more than 11% of mothers were estranged from at least one adult child.

    So, if you think of the ten or so houses nearest to you, probably at least one of them contains a parent estranged from at least one adult child. Maybe it’s yours. Either way, we hope this article will give you some pause for thought.

    Which way around?

    It makes a difference to the usefulness of this article whether any given reader experiencing estrangement is the parent or the adult child. We’re going to assume the reader is the parent. It also makes a difference who did the estranging. That’s usually the adult child.

    So, we’re broadly going to write with that expectation.

    Why does it happen?

    When our kids are small, we as parents hold all the cards. It may not always feel that way, but we do. We control our kids’ environment, we influence their learning, we buy the food they eat and the clothes they wear. If they want to go somewhere, we probably have to take them. We can even set and enforce rules on a whim.

    As they grow, so too does their independence, and it can be difficult for us as parents to relinquish control, but we’re going to have to at some point. Assuming we are good parents, we just hope we’ve prepared them well enough for the world.

    Once they’ve flown the nest and are living their own adult lives, there’s an element of inversion. They used to be dependent on us; now, not only do they not need us (this is a feature not a bug! If we have been good parents, they will be strong without us, and in all likelihood one day, they’re going to have to be), but also…

    We’re more likely to need them, now. Not just in the “oh if we have kids they can look after us when we’re old” sense, but in that their social lives are growing as ours are often shrinking, their family growing, while ours, well, it’s the same family but they’re the gatekeepers to that now.

    If we have a good relationship, this goes fine. However, it might only take one big argument, one big transgression, or one “final straw”, when the adult child decides the parent is more trouble than they’re worth.

    And, obviously, that’s going to hurt. But it’s pretty much how it pans out, according to studies:

    Here be science: Tensions in the Parent and Adult Child Relationship: Links to Solidarity and Ambivalence

    How to fix it, step one

    First, figure out what went wrong.

    Resist any urge to protect your own feelings with a defensive knee-jerk “I don’t know; I was a good, loving parent”. That’s a very natural and reasonable urge and you’re quite possibly correct, but it won’t help you here.

    Something pushed them away. And, it will almost certainly have been a push factor from you, not a pull factor from whoever is in their life now. It’s easy to put the blame externally, but that won’t fix anything.

    And, be honest with yourself; this isn’t a job interview where we have to present a strength dressed up as a “greatest weakness” for show.

    You can start there, though! If you think “I was too loving”, then ok, how did you show that love? Could it have felt stifling to them? Controlling? Were you critical of their decisions?

    It doesn’t matter who was right or wrong, or even whether or not their response was reasonable. It matters that you know what pushed them away.

    How to fix it, step two

    Take responsibility, and apologize. We’re going to assume that your estrangement is such that you can, at least, still get a letter to them, for example. Resist the urge to argue your case.

    Here’s a very good format for an apology; please consider using this template:

    The 10-step (!) apology that’s so good, you’ll want to make a note of it

    You may have to do some soul-searching to find how you will avoid making the same mistake in the future, that you did in the past.

    If you feel it’s something you “can’t change”, then you must decide what is more important to you. Only you can make that choice, but you cannot expect them to meet you halfway. They already made their choice. In the category of negotiation, they hold all the cards now.

    How to fix it, step three

    Now, just wait.

    Maybe they will reply, forgiving you. If they do, celebrate!

    Just be aware that once you reconnect is not the time to now get around to arguing your case from before. It will never be the time to get around to arguing your case from before. Let it go.

    Nor should you try to exact any sort of apology from them for estranging you, or they will at best feel resentful, wonder if they made a mistake in reconnecting, and withdraw.

    Instead, just enjoy what you have. Many people don’t get that.

    If they reply with anger, maybe it will be a chance to reopen a dialogue. If so, family therapy could be an approach useful for all concerned, if they are willing. Chances are, you all have things that you’d all benefit from talking about in a calm, professional, moderated, neutral environment.

    You might also benefit from a book we reviewed previously, “Parent Effectiveness Training”. This may seem like “shutting the stable door after the horse has bolted”, but in fact it’s a very good guide to relationship dynamics in general, and extensively covers relations between parents and adult children.

    If they don’t reply, then, you did your part. Take solace in knowing that much.

    Some final thoughts:

    At the end of the day, as parents, our kids living well is (hopefully) testament to that we prepared them well for life, and sometimes, being a parent is a thankless task.

    But, we (hopefully) didn’t become parents for the plaudits, after all.

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  • Learning to Love Midlife – by Chip Conley

    The 10almonds Team

    10almonds is reader-supported. We may, at no cost to you, receive a portion of sales if you purchase a product through a link in this article.

    While the book is titled about midlife, it could have said: midlife and beyond.

    Some of the benefits discussed in this book really only kick in during one’s 50s, 60s, or 70s, usually. Which, for all but the most optimistic, is generally considered to be stretching beyond what is usually called “midlife”.

    However! Chip Conley makes the argument for midlife being anywhere from one’s early 30s to mid-70s, depending on what (and how) we’re doing in life.

    He talks about (as the subtitle promises) 12 reasons life gets better with age, and those reasons are grouped into 5 categories, thus:

    1. Physical life
    2. Emotional life
    3. Mental life
    4. Vocational life
    5. Spiritual life

    It may surprise some readers that there are physical benefits that come with aging, but we do get two chapters in that category.

    The writing style is very casual, yet with references to science throughout, and a bibliography for such.

    Bottom line: if you’d like to make sure you’re making the most of your midlife and beyond, this a book that offers a lot of guidance on doing so!

    Click here to check out Learning to Love Midlife, and age in style!

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Related Posts

  • The Many Health Benefits Of Garlic

  • The Vagus Nerve’s Power for Weight Loss

    10almonds is reader-supported. We may, at no cost to you, receive a portion of sales if you purchase a product through a link in this article.

    The 10almonds Team

    Dr. Arun Dhir is a university lecturer, a gastrointestinal surgeon, an author, and a yoga and meditation instructor, and he has this to say:

    Gut feelings

    The vagus nerve is the 10th cranial nerve, also known as “vagus” (“the wanderer”), because it travels from the brain to many other body parts, including the ears, throat, heart, respiratory system, gut, pancreas, liver, and reproductive system. It’s no surprise then, that it plays a key role in brain-gut communication and metabolism regulation.

    The vagus nerve is part of the parasympathetic nervous system, responsible for rest, digestion, and counteracting the stress response. Most signals through the vagus nerve travel from the gut to the brain, though there is communication in both directions.

    You may be beginning to see how this works and its implications for weight management: the vagus nerve senses metabolites from the liver, pancreas, and small intestine, and regulates insulin production by stimulating beta cells in the pancreas, which is important for avoiding/managing insulin resistance and metabolic syndrome in general.

    Dr. Dhir cites a study in which vagus nerve stimulation (originally used for treating epilepsy and depression) was shown to cause unintentional weight loss (6-11%) in patients, revealing a link to weight management. Of course, that is quite a specific sample, so more research is needed to say for sure, but because the principle is very sound and the mechanism of action is clear, it’s not being viewed as a controversial conclusion.

    As for how get these benefits, here are seven ways:

    1. Cold water on the face: submerge your face in cold water in the morning while holding water in your mouth, or cover your face with a cold wet washcloth (while holding your breath please; no need to waterboard yourself!), which activates the “mammalian dive response” in which your body activates the parasympathetic nervous system in order to remain calm and thus survive for longer underwater
    2. Alternate hot and cold showers: switch between hot and cold water during showers for 10-second intervals; this creates eustress and activates the process of hormesis, improving your overall stress management and reducing any chronic stress response you may otherwise have going on
    3. Humming and gargling: the vibrations in the throat stimulate the nearby vagus nerve
    4. Deep breathing (pranayama): yoga breathing exercises, especially combined with somatic exercises such as the sun salutation, can stimulate the vagus nerve
    5. Intermittent fasting: helps recalibrate the metabolism and indirectly improves vagus nerve function
    6. Massage and acupressure: stimulates lymphatic channels and the vagus nerve
    7. Long walks in nature (“forest bathing”): helps trigger relaxation in general

    For more on all of this, enjoy:

    Click Here If The Embedded Video Doesn’t Load Automatically!

    Want to learn more?

    You might also like to read:

    The Vagus Nerve (And How You Can Make Use Of It)

    Take care!

    Don’t Forget…

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  • Healthy Mind In A Healthy Body

    10almonds is reader-supported. We may, at no cost to you, receive a portion of sales if you purchase a product through a link in this article.

    The 10almonds Team

    The 8-minute piece of music “Weightless” by Marconi was created scientifically to lower the heart rate and relax the listener. How did they do it? You can read the British Academy of Sound Therapy’s explanation of the methodology here, but important results of the study were:

    • “Weightless” was able to induce greater relaxation levels than a massage (increase of 6%).
    • “Weightless” also induced an 11% increase in relaxation over all other relaxing music tracks in the study.
    • “Weightless” was also subjectively rated as more relaxing than any other music by all the participants.

    Try it for yourself!

    Click Here If The Embedded Video Doesn’t Load Automatically!

    Isn’t that better? Whenever you’re ready, read on…

    Today we’re going to share a technique for dealing with difficult emotions. The technique is used in Cognitive Behavioral Therapy (CBT), and Dialectical Behavior Therapy (DBT), and it’s called RAIN:

    • Recognizing: ask yourself “what is it that I’m feeling?”, and put a name to it. It could be anger, despair, fear, frustration, anxiety, overwhelm etc.
    • Accepting: “OK, so, I’m feeling ________”. There’s no point in denying it, or being defensive about it, these things won’t help you. For now, just accept it.
    • Investigating: “Why am I feeling ________?” Maybe there is an obvious reason, maybe you need to dig for a reason—or dig deeper for the real reason. Most bad feelings are driven by some sort of fear or insecurity, so that can be a good avenue for examination. Important: your feelings may be rational or irrational. That’s fine. This is a time for investigating, not judging.
    • Non-Identification: not making whatever it is you’re feeling into a part of you. Once you get too attached to “I am jealous”, “I am angry”, “I am sad” etc, it can be difficult to manage something that has become a part of your personality; you’ll defend your jealousy, anger, sadness etc rather than tackle it.

    As a CBT tool, this is something you can do for yourself at any time. It won’t magically solve your problems, but it can stop you from spiralling into a state of crisis, and get you back on a more useful track.

    As a DBT tool, to give this its full strength, ideally now you will communicate what you’re feeling, to somebody you trust, perhaps a partner or friend, for instance.

    Humans are fundamentally social creatures, and we achieve our greatest strengths when we support each other—and that also means sometimes seeking and accepting support!

    Do you have a good technique you’d like to share? Reply to this email and let us know!

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  • Driving under the influence of marijuana: An explainer and research roundup

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    Naseem S. Miller – The Journalist's Resource

    Update 1: On May 16, 2024, the U.S. Department of Justice sent a proposed rule to the Federal Register to downgrade marijuana from a Schedule I to a Schedule III drug. This is the first step in a lengthy approval process that starts with a 60-day comment period.

    Update 2: Two recent research studies were added to the “Studies on marijuana and driving” section of this piece on July 18, 2024.

    As marijuana use continues to rise and state-level marijuana legalization sweeps the U.S., researchers and policymakers are grappling with a growing public safety concern: marijuana-impaired driving.

    As of April 2023, 38 U.S. states had legalized medical marijuana and 23 had legalized its recreational use, according to the National Conference of State Legislatures. Recreational or medical marijuana measures are on the ballot in seven states this year.

    The issue of marijuana-impaired driving has not been an easy one to tackle because, unlike alcohol, which has well-established thresholds of impairment, the metrics for marijuana’s effects on driving remain rather elusive.

    “We don’t have that kind of deep knowledge right now and it’s not because of lack of trying,” says Dr. Guohua Li, professor of epidemiology and the founding director of the Center for Injury Science and Prevention at Columbia University.

    “Marijuana is very different from alcohol in important ways,” says Li, who has published several studies on marijuana and driving. “And one of them is that the effect of marijuana on cognitive functions and behaviors is much more unpredictable than alcohol. In general, alcohol is a depressant drug. But marijuana could act on the central nervous system as a depressant, a stimulant, and a hallucinogenic substance.”

    Efforts to create a breathalyzer to measure the level of THC, the main psychoactive compound found in the marijuana plant, have largely failed, because “the THC molecule is much bigger than ethanol and its behavior after ingestion is very different from alcohol,” Li says.

    Currently, the two most common methods used to measure THC concentration to identify impaired drivers are blood and saliva tests, although there’s ongoing debate about their reliability.

    Marijuana, a term interchangeably used with cannabis, is the most commonly used federally illegal drug in the U.S.: 48.2 million people, or about 18% of Americans reported using it at least once in 2019, according to the latest available data from the Centers for Disease Control and Prevention. Worldwide, 2.5% of the population consumes marijuana, according to the World Health Organization.

    Marijuana is legal in several countries, including Canada, where it was legalized in 2018. Despite state laws legalizing cannabis, it remains illegal at the federal level in the U.S.

    As states grapple with the contentious issue of marijuana legalization, the debate is not just about public health, potential tax revenues and economic interests. At the heart of the discussion is also the U.S. criminal justice system.

    Marijuana is shown to have medicinal qualities and, compared with substances like alcohol, tobacco, and opioids, it has relatively milder health risks. However, it’s not risk-free, a large body of research has shown.

    Marijuana consumption can lead to immediate effects such as impaired muscle coordination and paranoia, as well as longer-term effects on mental health and cognitive functions — and addiction. As its use becomes more widespread, researchers are trying to better understand the potential hazards of marijuana, particularly for younger users whose brains are in critical stages of development.

    Marijuana and driving

    The use of marijuana among drivers, passengers and pedestrians has increased steadily over the past two decades, Li says.

    Compared with the year 2000, the proportion of U.S. drivers on the road who are under the influence of marijuana has increased by several folds, between five to 10 times, based on toxicology testing of people who died in car crashes, Li says.

    A 2022 report from the National Transportation Safety Board finds alcohol and cannabis are the two most commonly detected drugs among drivers arrested for impaired driving and fatally injured drivers. Most drivers who tested positive for cannabis also tested positive for another potentially impairing drug.

    “Although cannabis and many other drugs have been shown to impair driving performance and are associated with increased crash risk, there is evidence that, relative to alcohol, awareness about the potential dangers of driving after using other drugs is lower,” according to the report.

    Indeed, many U.S. adults perceive daily marijuana use or exposure to its smoke safer than tobacco, even though research finds otherwise.

    Several studies have demonstrated marijuana’s impact on driving.

    Marijuana use can reduce the drivers’ ability to pay attention, particularly when they are performing multiple tasks, research finds. It also slows reaction time and can impair coordination.

    “The combination is that you potentially have people who are noticing hazards later, braking slower and potentially not even noticing hazards because of their inability to focus on competing things on the road,” says Dr. Daniel Myran, an assistant professor at the Department of Family Medicine and health services researcher at the University of Ottawa.

    In a study published in September in JAMA Network Open, Myran and colleagues find that from 2010 to 2021 the rate of cannabis-involved traffic injuries that led to emergency department visits in Ontario, Canada, increased by 475%, from 0.18 per 1,000 traffic injury emergency department visits in 2010 to 1.01 visits in 2021.

    To be sure, cannabis-involved traffic injuries made up a small fraction of all traffic injury-related visits to hospital emergency departments. Out of 947,604 traffic injury emergency department visits, 426 had documented cannabis involvement.

    Myran cautions the increase shouldn’t be solely attributed to marijuana legalization. It captures changing societal attitudes toward marijuana and acceptance of cannabis use over time in the lead-up to legalization. In addition, it may reflect an increasing awareness among health care providers about cannabis-impaired driving, and they may be more likely to ask about cannabis use and document it in medical charts, he says.

    “When you look at the 475% increase in cannabis involvement in traffic injuries, rather than saying legalizing cannabis has caused the roads to be unsafe and is a public health disaster, it’s that cannabis use appears to be growing as a risk for road traffic injuries and that there seem to be more cannabis impaired drivers on the road,” Myran says. “Legalization may have accelerated this trend. Faced with this increase, we need to think about what are public health measures and different policy interventions to reduce harms from cannabis-impaired driving.”

    Setting a legal limit for marijuana-impaired driving

    Setting a legal limit for marijuana-impaired driving has not been easy. Countries like Canada and some U.S. states have agreed upon a certain level of THC in blood, usually between 1 to 5 nanograms per milliliter. Still, some studies have found those limits to be weak indicators of cannabis-impaired driving.

    When Canada legalized recreational marijuana in 2018, it also passed a law that made it illegal to drive with blood THC levels of more than 2 nanograms. The penalties are more severe for blood THC levels above 5 nanograms. The blood test is done at the police station for people who are pulled over and are deemed to be drug impaired.

    In the U.S., five states — Ohio, Illinois, Montana, Washington and Nevada — have “per se laws,” which set a specific amount of THC in the driver’s blood as evidence of impaired driving, according to the National Conference of State Legislatures. That limit ranges between 2 and 5 nanograms of THC per milliliter of blood.

    Colorado, meanwhile, has a “permissible inference law,” which states that it’s permissible to assume the driver was under the influence if their blood THC level is 5 nanograms per milliliter or higher, according to NCSL.

    Twelve states, most which have legalized some form of marijuana of use, have zero tolerance laws for any amount of certain drugs, including THC, in the body.

    The remaining states have “driving under the influence of drugs” laws. Among those states, Alabama and Michigan, have oral fluid roadside testing program to screen drivers for marijuana and other drugs, according to NCSL.

    In May this year, the U.S. Department of Transportation published a final rule that allows employers to use saliva testing for commercially licensed drivers, including truck drivers. The rule, which went into effect in June, sets the THC limit in saliva at 4 nanograms.

    Saliva tests can detect THC for 8 to 24 hours after use, but the tests are not perfect and can results in false positives, leading some scientists to argue against using them in randomly-selected drivers.

    In a 2021 report, the U.S. National Institute of Justice, the research and development arm of the Department of Justice, concluded that THC levels in bodily fluids, including blood and saliva “were not reliable indicators of marijuana intoxication.”

    Studies on marijuana and driving

    Over the past two decades, many studies have shown marijuana use can impair driving. However, discussions about what’s the best way to measure the level of THC in blood or saliva are ongoing. Below, we highlight and summarize several recent studies that address the issue. The studies are listed in order of publication date. We also include a list of related studies and resources to inform your audiences.

    State Driving Under the Influence of Drugs Laws
    Alexandra N. Origenes, Sarah A. White, Emma E. McGinty and Jon S. Vernick. Journal of Law, Medicine & Ethics, July 2024.

    Summary: As of January 2023, 33 states and D.C. had a driving under the influence of drugs law for at least one drug other than cannabis. Of those, 29 states and D.C. had a law specifically for driving under the influence of cannabis, in addition to a law for driving under the influence of other drugs. Four states had a driving under the influence of drug laws, excluding cannabis. Meanwhile, 17 states had no law for driving under the influence of drugs, including cannabis.  “The 17 states lacking a DUID law that names specific drugs should consider enacting such a law. These states already have expressed their concern — through legislation — with drug-impaired driving. However, failure to name specific drugs is likely to make the laws more difficult to enforce. These laws may force courts and/or law enforcement to rely on potentially subjective indicators of impairment,” the authors write.

    Associations between Adolescent Marijuana Use, Driving After Marijuana Use and Recreational Retail Sale in Colorado, USA
    Lucas M. Neuroth, et al. Substance Use & Misuse, October 2023.

    Summary: Researchers use data from four waves (2013, 2015, 2017 and 2019) of the Healthy Kids Colorado Survey, including 47,518 students 15 and older who indicated that they drove. They find 20.3% of students said that they had used marijuana in the past month and 10.5% said they had driven under the influence of marijuana. They find that the availability of recreational marijuana in stores was associated with an increased prevalence of using marijuana one to two times in the past month and driving under the influence of marijuana at least once. “Over the study period, one in ten high school age drivers engaged in [driving after marijuana use], which is concerning given the high risk of motor vehicle-related injury and death arising from impaired driving among adolescents,” the authors write.

    Are Blood and Oral Fluid Δ9-tetrahydrocannabinol (THC) and Metabolite Concentrations Related to Impairment? A Meta-Regression Analysis
    Danielle McCartney, et al. Neuroscience & Biobehavioral Reviews, March 2022.

    Summary: Commonly used THC measurements may not be strong indicators of driving impairment. While there is a relationship between certain biomarkers like blood THC concentrations and impaired driving, this correlation is often weak. The study underscores the need for more nuanced and comprehensive research on this topic, especially as cannabis usage becomes more widespread and legally accepted.

    The Effects of Cannabis and Alcohol on Driving Performance and Driver Behaviour: A Systematic Review and Meta-Analysis
    Sarah M. Simmons, Jeff K. Caird, Frances Sterzer and Mark Asbridge. Addiction, January 2022.

    Summary: This meta-analysis of experimental driving studies, including driving simulations, confirms that cannabis impairs driving performance, contrary to some beliefs that it might enhance driving abilities. Cannabis affects lateral control and speed — typically increasing lane excursions while reducing speed. The combination of alcohol and marijuana appears worse than either alone, challenging the idea that they cancel each other out.

    Cannabis Legalization and Detection of Tetrahydrocannabinol in Injured Drivers
    Jeffrey R. Brubacher, et al. The New England Journal of Medicine, January 2022.

    Summary: Following the legalization of recreational marijuana in Canada, there was a notable increase in injured drivers testing positive for THC, especially among those 50 years of age or older. This rise in cannabis-related driving incidents occurred even with new traffic laws aiming to deter cannabis-impaired driving. This uptick began before legalization became official, possibly due to perceptions that cannabis use was soon-to-be legal or illegal but not enforced. The data suggests that while legalization has broad societal impacts, more comprehensive strategies are needed to deter driving under the influence of cannabis and raise public awareness about its risks.

    Cannabis and Driving
    Godfrey D. Pearlson, Michael C. Stevens and Deepak Cyril D’Souza. Frontiers in Psychiatry, September 2021.

    Summary: Cannabis-impaired driving is a growing public health concern, and studies show that such drivers are more likely to be involved in car crashes, according to this review paper. Drivers are less affected by cannabis than they are by alcohol or cocaine, but the problem is expected to escalate with increasing cannabis legalization and use. Unlike alcohol, THC’s properties make it challenging to determine direct impairment levels from testing results. Current roadside tests lack precision in detecting genuine cannabis-impaired drivers, leading to potential wrongful convictions. Moreover, there is a pressing need for research on the combined effects of alcohol and cannabis on driving, as well as the impact of emerging popular forms of cannabis, like concentrates and edibles. The authors recommend public awareness campaigns about the dangers of driving under the influence of cannabis, similar to those against drunk driving, to address misconceptions. Policymakers should prioritize science-based decisions and encourage further research in this domain.

    Demographic And Policy-Based Differences in Behaviors And Attitudes Towards Driving After Marijuana Use: An Analysis of the 2013–2017 Traffic Safety Culture Index
    Marco H. Benedetti, et al. BMC Research Notes, June 2021.

    Summary: The study, based on a U.S. survey, finds younger, low-income, low-education and male participants were more tolerant of driving after marijuana consumption. Notably, those in states that legalized medical marijuana reported driving after use more frequently, aligning with studies indicating a higher prevalence of THC detection in drivers from these states. Overall, while the majority perceive driving after marijuana use as dangerous, not all research agrees on its impairment effects. Existing studies highlight that marijuana impacts motor skills and executive functions, yet its direct correlation with crash risk remains debated, given the variations in individual tolerance and how long THC remains in the system.

    Driving Under the Influence of Cannabis: A Framework for Future Policy
    Robert M. Chow, et al.Anesthesia & Analgesia, June 2019.

    Summary: The study presents a conceptual framework focusing on four main domains: legalization, driving under the influence of cannabis, driver impairment, and motor vehicle accidents. With the growing legalization of cannabis, there’s an anticipated rise in cannabis-impaired driving cases. The authors group marijuana users into infrequent users who show significant impairment with increased THC blood levels, chronic users with minimal impairment despite high THC levels, and those with consistent psychomotor deficits. Current challenges lie in the lack of standardized regulation for drivers influenced by cannabis, primarily because of state-to-state variability and the absence of a federal statutory limit for blood THC levels. European nations, however, have established thresholds for blood THC levels, ranging from 0.5 to 50.0 micrograms per liter depending on whether blood or blood serum are tested. The authors suggest the combined use of alcohol and THC blood tests with a psychomotor evaluation by a trained professional to determine impairment levels. The paper stresses the importance of creating a structured policy framework, given the rising acceptance and use of marijuana in society.

    Additional research

    Cannabis-Involved Traffic Injury Emergency Department Visits After Cannabis Legalization and Commercialization
    Daniel T. Myran, et al. JAMA Network Open, September 2023.

    Driving Performance and Cannabis Users’ Perception of Safety: A Randomized Clinical Trial
    Thomas D. Marcotte, et al. JAMA Psychiatry, January 2022.

    Medicinal Cannabis and Driving: The Intersection of Health and Road Safety Policy
    Daniel Perkins, et al. International Journal of Drug Policy, November 2021.

    Prevalence of Marijuana Use Among Trauma Patients Before and After Legalization of Medical Marijuana: The Arizona Experience
    Michael Levine, et al. Substance Abuse, July 2021.

    Self-Reported Driving After Marijuana Use in Association With Medical And Recreational Marijuana Policies
    Marco H. Benedetti, et al. International Journal of Drug Policy, June 2021.

    Cannabis and Driving Ability
    Eric L. Sevigny. Current Opinion in Psychology, April 2021.

    The Failings of per se Limits to Detect Cannabis-Induced Driving Impairment: Results from a Simulated Driving Study
    Thomas R. Arkell, et al. Traffic Injury Prevention, February 2021.

    Risky Driving Behaviors of Drivers Who Use Alcohol and Cannabis
    Tara Kelley-Baker, et al. Transportation Research Record, January 2021.

    Direct and Indirect Effects of Marijuana Use on the Risk of Fatal 2-Vehicle Crash Initiation
    Stanford Chihuri and Guohua Li. Injury Epidemiology, September 2020

    Cannabis-Impaired Driving: Evidence and the Role of Toxicology Testing
    Edward C. Wood and Robert L. Dupont. Cannabis in Medicine, July 2020.

    Association of Recreational Cannabis Laws in Colorado and Washington State With Changes in Traffic Fatalities, 2005-2017
    Julian Santaella-Tenorio, et al. JAMA Internal Medicine, June 2020.

    Marijuana Decriminalization, Medical Marijuana Laws, and Fatal Traffic Crashes in US Cities, 2010–2017
    Amanda Cook, Gregory Leung and Rhet A. Smith. American Journal of Public Health, February 2020.

    Cannabis Use in Older Drivers in Colorado: The LongROAD Study
    Carolyn G. DiGuiseppi, et al. Accident Analysis & Prevention, November 2019.

    Crash Fatality Rates After Recreational Marijuana Legalization in Washington and Colorado
    Jayson D. Aydelotte, et al. American Journal of Public Health, August 2017.

    Marijuana-Impaired Driving: A Report to Congress
    National Highway Traffic Safety Administration, July 2017

    Interaction of Marijuana And Alcohol on Fatal Motor Vehicle Crash Risk: A Case–Control Study
    Stanford Chihuri, Guohua Li and Qixuan Chen. Injury Epidemiology, March 2017.

    US Traffic Fatalities, 1985–2014, and Their Relationship to Medical Marijuana Laws
    Julian Santaella-Tenorio, et al. American Journal of Public Health, February 2017.

    Delays in DUI Blood Testing: Impact on Cannabis DUI Assessments
    Ed Wood, Ashley Brooks-Russell and Phillip Drum. Traffic Injury Prevention, June 2015.

    Establishing Legal Limits for Driving Under the Influence of Marijuana
    Kristin Wong, Joanne E. Brady and Guohua Li. Injury Epidemiology, October 2014.

    Cannabis Effects on Driving Skills
    Rebecca L. Hartman and Marilyn A. Huestis. Clinical Chemistry, March 2014.

    Acute Cannabis Consumption And Motor Vehicle Collision Risk: Systematic Review of Observational Studies and Meta-Analysis
    Mark Asbridge, Jill A. Hayden and Jennifer L. Cartwright. The BMJ, February 2012.

    Resources for your audiences

    The following resources include explainers from federal agencies and national organizations. You’re free to use images and graphics from federal agencies.

    This article first appeared on The Journalist’s Resource and is republished here under a Creative Commons license.

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