From Lupus To Arthritis: New Developments
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This week’s health news round-up highlights some things that are getting better, and some things that are getting worse, and how to be on the right side of both:
New hope for lupus sufferers
Lupus is currently treated mostly with lifelong medications to suppress the immune system, which is not only inconvenient, but also can leave people more open to infectious diseases. The latest development uses CAR T-cell technology (as has been used in cancer treatment for a while) to genetically modify cells to enable the body’s own immune system to behave properly:
Read in full: Exciting new lupus treatment could end need for lifelong medication
Related: How to Prevent (Or Reduce The Severity Of) Inflammatory Diseases
It’s in the hips
There are a lot of different kinds of hip replacements, and those with either delta ceramic or oxidised zirconium head with a highly cross-linked polyethylene liner/cup have the lowest risk of need for revision in the 15 years after surgery. This is important, because obviously, once it’s in there, you want it to be able to stay in there and not have to be touched again any time soon:
Read in full: Study identifies hip implant materials with the lowest risk of needing revision
Related: Nobody Likes Surgery, But Here’s How To Make It Much Less Bad
Sooner is better than later
Often, people won’t know about an unwanted pregnancy in the first six weeks, but for those who are able to catch it early, Very Early Medical Abortion (VEMA) offers a safe an effective way of doing so, with success rate being linked to earliness of intervention:
Read in full: Very early medication abortion is effective and safe, study finds
Related: What Might A Second Trump Presidency Look Like for Health Care?
Increased infectious disease risks from cattle farms
Many serious-to-humans infectious diseases enter the human population via the animal food chain, and in this case, bird flu becoming more rampant amongst cows is starting to pose a clear threat to humans, so this is definitely something to be aware of:
Read in full: Bird flu infects 1 in 14 dairy workers exposed; CDC urges better protections
Related: With Only Gloves To Protect Them, Farmworkers Say They Tend Sick Cows Amid Bird Flu
Herald of woe
Gut health affects most of the rest of health, and there are a lot of links between gut and bone health. In this case, an association has been found between certain changes in the gut microbiome, and subsequent onset of rheumatoid arthritis:
Read in full: Changes in gut microbiome could signal onset of rheumatoid arthritis
Related: Stop Sabotaging Your Gut
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Reflexology: What The Science Says
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How Does Reflexology Work, Really?
In Wednesday’s newsletter, we asked you for your opinion of reflexology, and got the above-depicted, below-described set of responses:
- About 63% said “It works by specific nerves connecting the feet and hands to various specific organs, triggering healing remotely”
- About 26% said “It works by realigning the body’s energies (e.g. qi, ki, prana, etc), removing blockages and improving health“
- About 11% said “It works by placebo, at best, and has no evidence for any efficacy beyond that”
So, what does the science say?
It works by realigning the body’s energies (e.g. qi, ki, prana, etc), removing blockages and improving health: True or False?
False, or since we can’t prove a negative: there is no reliable scientific evidence for this.
Further, there is no reliable scientific evidence for the existence of qi, ki, prana, soma, mana, or whatever we want to call it.
To save doubling up, we did discuss this in some more detail, exploring the notion of qi as bioelectrical energy, including a look at some unreliable clinical evidence for it (a study that used shoddy methodology, but it’s important to understand what they did wrong, to watch out for such), when we looked at [the legitimately very healthful practice of] qigong, a couple of weeks ago:
Qigong: A Breath Of Fresh Air?
As for reflexology specifically: in terms of blockages of qi causing disease (and thus being a putative therapeutic mechanism of action for attenuating disease), it’s an interesting hypothesis but in terms of scientific merit, it was pre-emptively supplanted by germ theory and other similarly observable-and-measurable phenomena.
We say “pre-emptively”, because despite orientalist marketing, unless we want to count some ancient pictures of people getting a foot massage and say it is reflexology, there is no record of reflexology being a thing before 1913 (and that was in the US, by a laryngologist working with a spiritualist to produce a book that they published in 1917).
It works by specific nerves connecting the feet and hands to various specific organs, triggering healing remotely: True or False?
False, or since we can’t prove a negative: there is no reliable scientific evidence for this.
A very large independent review of available scientific literature found the current medical consensus on reflexology is that:
- Reflexology is effective for: anxiety (but short lasting), edema, mild insomnia, quality of sleep, and relieving pain (short term: 2–3 hours)
- Reflexology is not effective for: inflammatory bowel disease, fertility treatment, neuropathy and polyneuropathy, acute low back pain, sub acute low back pain, chronic low back pain, radicular pain syndromes (including sciatica), post-operative low back pain, spinal stenosis, spinal fractures, sacroiliitis, spondylolisthesis, complex regional pain syndrome, trigger points / myofascial pain, chronic persistent pain, chronic low back pain, depression, work related injuries of the hip and pelvis
Source: Reflexology – a scientific literary review compilation
(the above is a fascinating read, by the way, and its 50 pages go into a lot more detail than we have room to here)
Now, those items that they found it effective for, looks suspiciously like a short list of things that placebo is often good for, and/or any relaxing activity.
Another review was not so generous:
❝The best evidence available to date does not demonstrate convincingly that reflexology is an effective treatment for any medical condition❞
~ Dr. Edzard Ernst (MD, PhD, FMedSci)
Source: Is reflexology an effective intervention? A systematic review of randomised controlled trials
In short, from the available scientific literature, we can surmise:
- Some researchers have found it to have some usefulness against chiefly psychosomatic conditions
- Other researchers have found the evidence for even that much to be uncompelling
It works by placebo, at best, and has no evidence for any efficacy beyond that: True or False?
Mostly True; of course reflexology runs into similar problems as acupuncture when it comes to testing against placebo:
How Does One Test Acupuncture Against Placebo Anyway?
…but not quite as bad, since it is easier to give a random foot massage while pretending it is a clinical treatment, than to fake putting needles into key locations.
However, as the paper we cited just above (in answer to the previous True/False question) shows, reflexology does not appear to meaningfully outperform placebo—which points to the possibility that it does work by placebo, and is just a placebo treatment on the high end of placebo (because the placebo effect is real, does work, isn’t “nothing”, and some placebos work better than others).
For more on the fascinating science and useful (applicable in daily life!) practicalities of how placebo does work, check out:
How To Leverage Placebo Effect For Yourself
Take care!
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To Nap Or Not To Nap; That Is The Question
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It’s Q&A Day at 10almonds!
Have a question or a request? We love to hear from you!
In cases where we’ve already covered something, we might link to what we wrote before, but will always be happy to revisit any of our topics again in the future too—there’s always more to say!
As ever: if the question/request can be answered briefly, we’ll do it here in our Q&A Thursday edition. If not, we’ll make a main feature of it shortly afterwards!
So, no question/request too big or small
❝Is it good to nap in the afternoon, or better to get the famous 7 to 9 hours at night and leave it at that? I’m worried that daytime napping to make up for a shorter night’s sleep will just perpetuate and worsen it in the long run, is there a categorical answer here?❞
Short version: generally considered best is indeed the 7–9 hours at night (yes, including at older ages):
Why You Probably Need More Sleep
…and sleep efficiency does matter too:
Why 7 Hours Sleep Is Not Enough
…which in turn, is influenced by factors other than just length and depth:
The 6 Dimensions Of Sleep (And Why They Matter)
However! Knowing what is best in theory does not help at all if it’s unattainable in practice. So, if you’re not getting a good night’s sleep (and we’ll assume you’re already practising good sleep hygiene; fresh bedding, lights-off by a certain time, no alcohol or caffeine before bed, that kind of thing), then a first port-of-call may be sleep remedies:
Safe Effective Sleep Aids For Seniors
If even those don’t work, then napping is now likely your best back-up option. But, napping done incorrectly can indeed cause as many problems as it solves. There’s a difference between:
- “I napped and now I have energy again” and you continue with your day
- “Darkness took me, and I strayed out of thought and time. Stars wheeled overhead, and every day was as long as the life age of the earth—but it was not the end.” and now you’re not sure whether it’s day or night, whose house you’re in, or whether you’ve been drugged.
These two very common napping experiences are influenced by factors that we can control:
How To Nap Like A Pro (No More “Sleep Hangovers”!)
If you still prefer to not risk napping but do need at least some kind of refreshment that’s actually a refreshment and not just taking stimulants, then you might consider this practice (from yoga nidra) that gives some of the same benefits of sleep, without actually sleeping:
Non-Sleep Deep Rest: A Neurobiologist’s Insights
Take care!
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Chiropractors have been banned again from manipulating babies’ spines. Here’s what the evidence actually says
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Chiropractors in Australia will not be able to perform spinal manipulation on children under the age of two once more, following health concerns from doctors and politicians.
But what is the spinal treatment at the centre of the controversy? Does it work? Is there evidence of harm?
We’re a team of researchers who specialise in evidence-based musculoskeletal health. I (Matt) am a registered chiropractor, Joshua is a registered physiotherapist and Giovanni trained as a physiotherapist.
Here’s what the evidence says.
Dmitry Naumov/Shutterstock Remind me, how did this all come about?
A Melbourne-based chiropractor posted a video on social media in 2018 using a spring-loaded device (known as the Activator) to manipulate the spine of a two-week-old baby suspended upside down by the ankles.
The video sparked widespread concerns among the public, medical associations and politicians. It prompted a ban on the procedure in young children. The Victorian health minister commissioned Safer Care Victoria to conduct an independent review of spinal manipulation techniques on children.
Recently, the Chiropractic Board of Australia reinstated chiropractors’ authorisation to perform spinal manipulation on babies under two years old. But this week, it backflipped, following heavy criticism from medical associations and politicians.
What is spinal manipulation?
Spinal manipulation is a treatment used by chiropractors and other health professionals such as doctors, osteopaths and physiotherapists.
It is an umbrella term that includes popular “back cracking” techniques.
It also includes more gentle forms of treatment, such as massage or joint mobilisations. These involve applying pressure to joints without generating a “cracking” sound.
Does spinal manipulation in babies work?
Several international guidelines for health-care professionals recommend spinal manipulation to treat adults with conditions such as back pain and headache as there is an abundance of evidence on the topic. For example, spinal manipulation for back pain is supported by data from nearly 10,000 adults.
For children, it’s a different story. Safer Care Victoria’s 2019 review of spinal manipulation found very few studies testing whether this treatment was safe and effective in children.
Studies were generally small and were of poor quality. Some of those small, poor-quality studies, suggest spinal manipulation provides a very small benefit for back pain, colic and potentially bedwetting – some common reasons for parents to take their child to see a chiropractor. But overall, the review found the overall body of evidence was very poor.
Spinal manipulation doesn’t seem to help young children with an ear infection. MIA Studio/Shutterstock However, for most other children’s conditions chiropractors treat – such as headache, asthma, otitis media (a type of ear infection), cerebral palsy, hyperactivity and torticollis (“twisted neck”) – there did not appear to be a benefit.
The number of studies investigating the effectiveness of spinal manipulation on babies under two years of age was even smaller.
There was one high-quality study and two small, poor quality studies. These did not show an appreciable benefit of spinal manipulation on colic, otitis media with effusion (known as glue ear) or twisted neck in babies.
Is spinal manipulation on babies safe?
In terms of safety, most studies in the review found serious complications were extremely rare. The review noted one baby or child dying (a report from Germany in 2001 after spinal manipulation by a physiotherapist). The most common complications were mild in nature such as increased crying and soreness.
However, because studies were very small, they cannot tell us anything about the safety of spinal manipulation in a reliable way. Studies that are designed to properly investigate if a treatment is safe typically include thousands of patients. And these studies have not yet been done.
Why do people see chiropractors?
Safer Care Victoria also conducted surveys with more than 20,000 people living in Australia who had taken their children under 12 years old to a chiropractor in the past ten years.
Nearly three-quarters said that was for treatment of a child aged two years or younger.
Nearly all people surveyed reported a positive experience when they took their child to a chiropractor and reported that their child’s condition improved with chiropractic care. Only a small number of people (0.3%) reported a negative experience, and this was mostly related to cost of treatment, lack of improvement in their child’s condition, excessive use of x-rays, and perceived pressure to avoid medications.
Many of the respondents had also consulted their GP or maternity/child health nurse.
What now for spinal manipulation in children?
At the request of state and federal ministers, the Chiropractic Board of Australia confirmed that spinal manipulation on babies under two years old will continue to be banned until it discusses the issue further with health ministers.
Many chiropractors believe this is unfair, especially considering the strong consumer support for chiropractic care outlined in the Safer Care Victoria report, and the rarity of serious reported harms in children.
Others believe that in the absence of evidence of benefit and uncertainty around whether spinal manipulation is safe in children and babies, the precautionary principle should apply and children and babies should not receive spinal manipulation.
Ultimately, high quality research is urgently needed to better understand whether spinal manipulation is beneficial for the range of conditions chiropractors provide it for, and whether the benefit outweighs the extremely small chance of a serious complication.
This will help parents make an informed choice about health care for their child.
Matt Fernandez, Senior lecturer and researcher in chiropractic, CQUniversity Australia; Giovanni E. Ferreira, NHMRC Emerging Leader Research Fellow, Institute of Musculoskeletal Health, University of Sydney, and Joshua Zadro, NHMRC Emerging Leader Research Fellow, Sydney Musculoskeletal Health, University of Sydney
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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Superfood-Stuffed Squash
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This stuffed squash recipe is packed with so many nutrient-dense ingredients, yet it feels delightfully decadent—a great recipe to have up your sleeve ready for fall.
You will need
- 1 large or two medium butternut squashes, halved lengthways and seeds removed (keep them; they are full of nutrients! You can sprout them, or dry them to use them at your leisure), along with some of the flesh from the central part above where the seeds are, so that there is room for stuffing
- 2 cups low-sodium vegetable stock
- 1 cup wild rice, rinsed
- 1 medium onion, finely chopped
- ½ cup walnuts, roughly chopped
- ½ cup dried
cranberriesgoji berries ← why goji berries? They have even more healthful properties than cranberries, and cranberries are hard to buy without so much added sugar that the ingredients list looks like “cranberries (51%), sugar (39%), vegetable oil (10%)”, whereas when buying goji berries, the ingredients list says “goji berries”, and they do the same culinary job. - ¼ cup pine nuts
- ½ bulb garlic, minced
- 1 tbsp dried thyme or 2 tsp fresh thyme, destalked
- 1 tbsp dried rosemary or 2 tsp fresh rosemary, destalked
- 1 generous handful fresh parsley, chopped
- 1 tbsp chia seeds
- 1 tbsp nutritional yeast
- 1 tbsp black pepper, coarse ground
- ½ tsp MSG or 1 tsp low-sodium salt
- Extra virgin olive oil, for brushing and frying
- Aged balsamic vinegar, to serve (failing this, make a balsamic vinegar reduction and use that; it should have a thicker texture but still taste acidic and not too sweet; the thickness should come from the higher concentration of grape must and its natural sugars; no need to add sugar)
Method
(we suggest you read everything at least once before doing anything)
1) Preheat the oven to 400°F / 200°C.
2) Brush the cut sides of the squash with olive oil; sprinkle with a pinch of MSG/salt and a little black pepper (grind it directly over the squash if you are using a grinder; hold the grinder high though so that it distributes evenly—waiters in restaurants aren’t just being dramatic when they do that with pepper or Parmesan or such)
3) Arrange them cut-sides-down on a baking tray lined with baking paper, and roast for at least 30 minutes or until tender.
4) While that is roasting, add the chia seeds to the wild rice, and cook them in the low-sodium vegetable stock, using a rice cooker if available. It should take about the same length of time, but if the rice is done first, set it aside, and if the squash is done first, turn the oven down low to keep it warm.
5) Heat some oil in a sauté pan (not a skillet without high sides; we’re going to need space in a bit), and fry the chopped onion until translucent and soft. We could say “about 5 minutes” but honestly it depends on your pan as well as the heat and other factors.
6) Add the seasonings (herbs, garlic, black pepper, MSG/salt, nooch), and cook for a further 2 minutes, stirring thoroughly to distribute evenly.
7) Add the rice, berries, and nuts, cooking for a further 2 minutes, stirring constantly, ensuring everything is heated evenly.
8) Remove the squash halves from the oven, turn them over, and spoon the mixture we just made into them, filling generously.
9) Drizzle a lashing of the aged balsamic vinegar (or balsamic vinegar reduction), to serve.
Enjoy!
Want to learn more?
For those interested in some of the science of what we have going on today:
- Brown Rice vs Wild Rice – Which is Healthier?
- Why You Should Diversify Your Nuts!
- Goji Berries: Which Benefits Do They Really Have?
- Chia: The Tiniest Seeds With The Most Value
- The Many Health Benefits Of Garlic
- Black Pepper’s Impressive Anti-Cancer Arsenal (And More)
- 10 Ways To Balance Blood Sugars
Take care!
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Super Gut – by Dr. William Davis
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You may be wondering: what sets this book apart from the other gut health books we’ve reviewed? For this one, mostly it’s depth.
This is the most scientifically dense book we’ve reviewed on gut health, so if you’re put off by that, this might not be one for you. However, you don’t need prior knowledge, as he does explain things as he goes. The advice in this book is not just the usual “gut health 101” stuff, either!
A particular strength of this book is that it looks at a wide variety of gut- and gut-related disorders, and ways certain readers may need to do different things than others, to address those problems on the path to good gut health.
The style, for all its hard science content, is quite sensationalist, and that may take some getting used to for non-Americans. However, it doesn’t affect the content!
Bottom line: if you just want simple basic advice, then probably best to skip this one. However, if you are sincerely serious about gut health (or just like reading this sort of thing because learning is satisfying), then this book is packed with relevant and detailed information.
Click here to check out Super Gut, and get to know and improve yours!
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Driving under the influence of marijuana: An explainer and research roundup
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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 2020Cannabis-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 2017Interaction 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.
- CDC’s main marijuana page.
- CDC’s marijuana data and statistics.
- Marijuana Drug Facts from the National Institute on Drug Abuse.
- Health Effects of Marijuana from the CDC.
- Learn About Marijuana Risks from the Substance Abuse and Mental Health Services Administration.
- Marijuana and Lung Health from the American Lung Association.
- Substance Use Disorder 101 from the U.S. Department of Health & Human Services.
- What You Need To Know About Marijuana Use and Driving from the CDC.
- Does marijuana use affect driving? from the National Institute on Drug Abuse.
- Drug-Impaired Driving from the National Highway Traffic Safety Administration.
This article first appeared on The Journalist’s Resource and is republished here under a Creative Commons license.
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