Proponents of marijuana legalization tout the drug’s safety and emphasize some of its medicinal properties. They have been successful in achieving legalization of marijuana in many jurisdictions, for medical and/or recreational use. Widespread use has enabled scientists to better understand two long-recognized safety concerns of the drug:
- Marijuana’s THC (∆9-tetrahydrocannabinol) impairs driving skills, and
- THC can be dangerous for young users.
We are bombarded daily with information, some of which is misleading, overly-simplified, or even outright false. Modern societies cherish free speech, yet when misinformation causes harm, it becomes imperative to set the record straight. When incorrect information about drug use is focused on vulnerable children, parents have an obligation to set that record straight.
Nearly all parents understand that children’s brains develop slowly and that eventually delightful children mature into wonderful adults. Except when they don’t. Yet relatively few parents understand that children’s brains typically don’t reach maturity until the mid to late 20s. Until that age, parents have both an opportunity and an obligation to ensure that their children do not succumb to incorrect information about the safety of marijuana use.
The facts summarized
THC impairs driving skills in a dose-related manner. The higher the dose, the more impaired an individual becomes. Driving impairment has been proven in laboratory experiments, driving simulators, and real-world driving experiments. It has been verified in analyses of traffic crashes, including fatal crashes. In spite of these facts, there are many contrary beliefs that circulate among marijuana users. We discuss many of these common beliefs and document the truth below.
THC can prevent youth’s brains from developing properly. This can result in addiction, cannabis induced psychosis, cannabis hyperemesis syndrome, schizophrenia, and suicides. Obviously, only a few youthful users develop these problems. The incidence is individualistic and unpredictable. However, we do know that long-term frequent use of high THC concentration products that are now available increases risks to the developing brain. Some youthful users simply lose intelligence, cognitive ability and mental executive function due to frequent THC use. As people mature, they become less susceptible to cannabis induced permanent brain damage, but remain subject to the impairing effects of THC on performance of many of life’s activities, including driving.
Common youth beliefs – driving
- Marijuana does not impair driving ability.
That belief is not true. THC causes a decline in motor performance resulting in delayed reaction times and a reduced ability to stay in one’s own driving lane. Cognitive functions decline which reduces one’s ability to maintain sustained attention to driving conditions, leads to poor decision-making, impulse control and memory .
Many marijuana users are comforted by the fact that the average “stoned” driver is less dangerous than the average drunk driver. But not all drivers are average. Since the level of impairment depends, among other things, on the dose of THC or alcohol consumed, it should come as no surprise that someone on a high dose of THC is more dangerous than someone on a low dose of alcohol.
- Driving under the influence of marijuana is safe because drivers go more slowly and avoid risky situations.
This myth is supported by a scene from Cheech and Chong’s movie “Up in Smoke,” but little else. Subjects in some driving simulator studies were fairly self-aware of the impairment caused by THC and drove more slowly. But those subjects were much less successful in compensating for their impairment under emergency driving conditions. Researchers concluded that simulator studies were only able to show how marijuana users were able to drive after using the drug in monitored conditions, rather than how they actually drove in the real world.
Both the California State Patrol and the Colorado State Patrol have reported that speeding, not slow driving, was the most common reason for stopping a driver who was ultimately arrested for driving under the influence of marijuana.
- Stoned driving is safer than drunk driving
Statistically that is true, but statistics are of no consolation to a parent who had lost a child due to driving under the influence of THC.
Multiple epidemiological studies have determined the relative risk or Odds Ratio (OR) of fatal crashes after using alcohol, THC, or a combination of both. Of those three conditions, the risk of a fatal crash is highest for drivers using a combination of alcohol and THC and the lowest for THC alone . The wide range of results seen from similar studies by different researchers speaks to the difficulty of conducting such studies reliably. Yet nearly all found that THC alone increases the risk of a fatal crash.
Just because stoned driving can be safer than drunk driving doesn’t mean one should drive stoned. After all, a .22 caliber bullet is about half as deadly as a 9 mm bullet, which in turn is about half as deadly as a .45 caliber bullet. That does not mean we should shoot people with .22 caliber bullets because it’s safe.
- A US government study proved that stoned driving does not increase crash risk.
This oft-quoted statement refers to a Virginia Beach study sponsored by NHTSA and summarized in 2015. The final and more detailed report was issued a year later. The study failed to find a statistically significant link between car crashes and THC presence. But a failure to find a link is not the same as finding that there is no link. It’s like your failure to find your car keys doesn’t mean that the keys no longer exist.
The Virginia Beach study failed to find a statistically significant link between car crashes and any drug or drug combination with the exception of alcohol, even though other drugs found, such as cocaine, methamphetamine, benzodiazepines, and opiates are even more impairing than THC. This was because NHTSA did not design the study to find statistically significant links between crash risk and drug use in the first place. Governmental incompetence is not limited to Congress. Note the following flaws in the study design:
- The sample size was too small to determine statistically significant links with the low baseline prevalence of drug use in Virginia City and the lower risk posed by drugs other than alcohol.
- The study site had only a 14.4% prevalence of drug use compared with a 19-22% prevalence in the rest of the United States.
- The study only included drivers who volunteered to participate. It’s not clear why a drug user involved in a crash would volunteer to participate. That limitation created a downward bias to the result.
- The study pool included not only the at-fault drivers in crashes, but also drivers who were innocent victims of an at-fault driver. That created a downward bias to the result.
- Freeway traffic was excluded from the study, so only 15 fatal crashes were included. That created downward bias to the result.
- Smoking a joint can sober someone up after drinking.
This is a dangerous myth. In fact, the combination of THC and alcohol is much more dangerous than impairment by either alcohol alone or marijuana alone as noted in #3 above.
- Chronic users build up a tolerance for THC, so they don’t become impaired.
Chronic users build up a tolerance to some, but not all of the effects of THC. After all, if they were tolerant to all of its effects, why would they keep using it? To compensate for their tolerance, chronic users consume higher quantities of a drug to obtain their desired effect. Chronic users tend to not exhibit as much motor control impairment as occasional users, and as a result will not have as much delayed reaction times or lane weaving as an occasional user. But their executive function is still highly impaired, leading to a similar loss in judgment, memory and problem solving as occasional users.
Rather than becoming immune to THC impairment, chronic users exhibit a blunted impairment compared to occasional users.
- Drivers aren’t impaired if their THC blood level is below 5 ng/mL.
This is not true. THC 5 ng/mL per se limits were determined by politicians and unlike alcohol per se limits, are not supported by science. Unlike with alcohol, there is no correlation between THC blood concentration and the level of impairment. Colorado arrested 991drivers for DUI in 2017 with a THC blood content below 5 ng/ml. 74.9% were found guilty.
- There is no test for marijuana impairment.
That is not true. Marijuana impairment tests rely upon behavioral assessments, rather than chemical assessments. Behavioral assessments are accurate but require time and training to administer.
Chemical tests are useful but are not required to convict someone of driving under the influence. They also prove drug use, but cannot prove impairment. Nationally, 24% of drivers arrested for DUI refuse chemical testing, yet they are still prosecuted and convicted.
Forensically determining impairment is akin to diagnosing an illness. A physician studies both symptoms and laboratory tests in making a diagnosis and devising a treatment plan. Police also rely upon symptoms and chemical tests to determine impairment and to prove impairment in court. Just as some disease diagnoses are straightforward and others more challenging, effectiveness of impairment assessments varies depending on the impairing substance(s), dose and symptoms. For alcohol, symptomatic assessment is easy and chemical assays are definitive. For marijuana, symptomatic assessment is much more difficult and chemical assays cannot prove or disprove impairment but can only confirm the drug responsible for the observed and documented impairment.
There are three common levels of impairment detection training provided to law enforcement officers: SFST (Standardized Field Sobriety Test), ARIDE (Advanced Roadside Impaired Driving Enforcement) and DRE (Drug Recognition Expert).
An SFST assessment can be completed within 5 minutes on-site, whereas a DRE assessment requires an average of 45 minutes in a controlled environment. SFST training takes about 3 days and is provided to all officers to qualify to make impaired driving arrests. ARIDE requires an additional 2 days of training. DRE requires an additional 2-3 weeks of difficult training and is not suitable for all officers.
Whereas the SFST battery of tests is well validated for detecting alcohol impairment, it is only moderately successful in detecting THC impairment. However, by adding two additional tools, finger-to-nose (FTN) and Modified Romberg Balance (MRB) to the standard three tools in SFST, officers can achieve a 96.7% reliability in detecting THC impairment.
- THC impairment is like alcohol impairment.
While there is an overlap in symptoms, THC impairment presents different symptoms than alcohol impairment.
The following symptoms are common to both alcohol and THC impairment: control loss, inability to process changes, loss of divided attention ability, loss of concentration, lane weaving, increased reaction time.
The following symptoms are either unique to or are more pronounced with alcohol impairment: lowered inhibitions, faster driving, decline in visual and auditory perceptions and processing functions.
The following symptoms are either unique to or are more pronounced with THC impairment: attempted compensation, caution in experimental settings, can perform simple tasks effectively, but exhibit impaired higher level cognitive functions.
- Stoned driving isn’t dangerous. I don’t know anyone killed by a marijuana-impaired driver.
You know people who smoke, right? Do you also know people killed by lung cancer? No? So by your logic smoking doesn’t cause lung cancer?
The problem we’re dealing with is a poor understanding of statistics. Both lung cancer and traffic deaths are fairly rare: approximately 135,000 lung cancer fatalities and 38,000 traffic fatalities per year in the US.
The best way of looking at traffic deaths is deaths per mile driven, shown below. The number has been dropping for the last 4 decades until recently since marijuana started being legalized. It was over 3 deaths per 100 million vehicle miles traveled and was 1.13 in 2018, the last year reported.
Someone who drives 20,000 miles per year from age 16 until retirement will drive 1 million miles in a lifetime. That driver would, on average, experience a traffic fatality every 88 lifetimes (100/1.13).
A drunk driver has a much higher risk of traffic fatalities. According to crash risk studies of alcohol-impaired drivers, someone who consistently drives with a BAC of .08, the per se limit of most states, would increase the risk of a traffic fatality to every 9 lifetimes. No wonder it’s so hard to stop drunk driving. Drunks believe they can get away with it. And they can. Until they don’t.
A stoned driver has a lower risk of traffic fatality than a drunk driver. Depending on which estimate you choose to believe, the relative risk may range from 2 to 10. If the relative risk is on the low end of about 2, that would mean a traffic fatality every 44 lifetimes.
You’re fortunate if you haven’t met someone like Steven Ryan, Timothy Durden, Makia Milton, Mark Hendrixson, Zachary LeMaster, Unises Nuñez, Kyle Couch or John Spence who killed innocent victims while driving stoned. It’s not because driving stoned is safe, it’s just that the statistics haven’t caught up with you yet.
Common youth beliefs – marijuana’s health effects
- Marijuana is a medicine. Therefore it’s safe to use.
Several states in the US have approved marijuana for medicinal use. But the FDA has not approved marijuana as a medicine. Physicians risk losing their license if they prescribe marijuana, but they are permitted to recommend it in states that allow its use.
Canada has approved the use of marijuana for medicinal purposes. But marijuana has not been approved as a medicine by the Health Products and Food Branch of Health Canada.
- No one has died from marijuana use, unlike heroin use.
Marijuana cannot cause respiratory arrest like heroin, but that doesn’t mean users have not died from its use. Marijuana users have died from both suicides as well as crashes and accidents caused by marijuana’s THC. Cannabis Hyperemesis syndrome has also occasionally proven fatal.
Most of the adverse health effects of marijuana use (addiction, psychosis, schizophrenia, suicides and cannabis hyperemesis syndrome) are concentrated in young users. Once a person’s brain has matured, typically in their mid-20s, they become less susceptible to cannabis induced psychosis, schizophrenia and suicides. Adults are also less susceptible to addiction than youths.
Parents have an obligation to protect their children from harm. Skinned knees are a part of growing up. Permanent brain damage is not. Children learn to alter their behavior to avoid skinned knees. The painful effects of injuries sustained from falling down are immediate and self-reinforcing. Effects of drug use on brain development are more gradual; there is no immediate self-reinforcing effect that tells someone to quit harming themselves.
Children learn from parents, their friends, advertisers, the media, their teachers, and many others. Some instructors have children’s best interests in mind. Others such as drug dealers and drug users do not. It is important for parents to educate their children to avoid use of drugs, especially in their early years, because they will receive lots of temptations from others to ‘experiment’ with drugs.
Common refrains from parents who have lost children to drug use, including marijuana use:
- I didn’t know it was dangerous.
- I didn’t know he/she was using drugs.
- By the time I found out how serious the problem was, the permanent damage was done.
- My parental influence was less powerful than addiction.
Parents have obligations to teach, to listen, to observe, and to love their children. There are many tools at parents’ disposal to teach, listen and to observe. Sharing the documented information above with children is one such tool. Closely observing behavior changes is another. Parents should also consider the use of home diagnostic tests to know if a child is using drugs. This can be especially important as a child is starting to drive. Requiring a simple, non-invasive negative drug test to borrow the family car can be an effective tool to stress the importance of avoiding drug use by youth. It just might save a life.
 Some prefer the term “cannabis” to “marijuana,” perhaps because it sounds more scientific or less pejorative. We’ve chosen to refer to the active drug compound THC (∆9-tetrahydrocannabinol), or to use the more traditional and common name of marijuana. Merriam-Webster defines marijuana as “ the psychoactive dried resinous flower buds and leaves of the female hemp or cannabis plant that contain high levels of THC.” Our concern here is with THC, not with the cannabis plant which, depending upon its strain may or may not produce marijuana or even contain appreciable amounts of THC.
 Sewell RA, Poling J, Sofuoglu M. The Effects of Cannabis Compared with Alcohol on Driving. Am J Addict. (2009); 18(3) 185-193
 Hartman RL, Huestis MA. Cannabis Effects on Driving Skills. Clin Chem 59:3 478-492 (2013)
 Broyd SJ, van Hell HH, Beale C, Yücel M, Solowij N. Acute and Chronic Effects of Cannabinoids on Human Cognition – A Systematic Review. Biological Psychiatry April 1, (2016) 79:557-567
 Hartman RL (2013) op.cit.
 Hartman RL, Brown TL, Milavetz et al. Cannabis effects on driving lateral control with and without alcohol. Drug and Alcohol Dependence Sept 1 (2015), 154: 25-37
 Hartman RL (2013) op.cit.
 Sewell RA op.cit.
 Ramaekers JG, Theunissen EL, de Bruwer M et al. Tolerance and cross-tolerance to neurocognitive effects of THC and alcohol in heavy cannabis users. Psychopharmacology DOI 10.1007/s0023-010-2042-1 (2010)
 Sewell RA op.cit.
 Braga AA, Cook PJ. The Association of Firearm Caliber with Likelihood of Death from Gunshot Injury in Criminal Assaults. JAMA Network Open. (2018);1(3)
 Compton RP, Berning A. Drug and Alcohol Crash Risk. NHTSA Traffic Safety Facts Research Note DOT HS 812 117 (2015)
 Lacey JH, Kelley-Baker T, Berning A et al. Drug and Alcohol Crash Risk: A Case-Control Study. Dec (2016) DOT HS 812 355 NHTSA
 Bogstrand ST, Gjerde H. Which drugs are associated with highest risk for being arrested for driving under the influence? A case-control study. Forensic Sci Int’l 240 (2014) 21-28
 Wood E. Weakest In the Nation: Colorado’s DUID laws are the weakest in the nation; why and how to fix that. (2018) Amazon
 Ramaekers JG, Kauert G, Theunisse EL et al. Neurocognitive performance during acute THC intoxication in heavy and occasional cannabis users. J Psychopharmacology 23 (3) (2009) 266-277
 Ramaekers JG, van Wel JH, Spronk DB. Cannabis and tolerance: acute drug impairment as a function of cannabis use history. Scientific Reports Nature 6: 26843 (2016)
 Solowij N. Peering Through the Haze of Smoked vs Vaporized Cannabis – To Vape or Not to Vape?. JAMA Open (2018); 1(7):e1848838
 Bui B, Reed J. Driving Under the Influence of Drugs and Alcohol. Colorado Department of Public Safety. June (2019)
 Namuswe ES, Coleman HL, Berning A. Breath Test Refusal Rates in the United States – 2011 Update. NHTSA DOT HS 811 881 (2014)
 Hartman RL, Richman JE, Hayes CE. Drug Recognition Expert (DRE) examination characteristics of cannabis impairment. Accident Analysis and Prevention 92 (2016) 219-229
 Huestis MA. Effects of cannabis with and without alcohol on driving. ACMT Seminars in Forensic Toxicology. Denver, CO, Dec 9, (2015)
 Greydanus DE and Cabral MD. Cannabis and the Teen Brain. In Chapter 5 of Cannabis in Medicine: An Evidence-Based Approach, Ken Finn, ed. Springer (2020) ISBN 978-3-030-45967-3