Neal Smith


Personal responsibility and common sense are the only real answers to whether someone should intake Marijuana and drive or not.

Come to think of it, personal responsibility and common sense need to be used any time you drive. Lack of sleep, stress, physical injuries or disabilities, even a head cold can play a negative role.

This is another area where emotion and politics has trumped science, reason and common sense. Yet, there are caveats in whether one should smoke Marijuana and drive an automobile or operate dangerous equipment. Law makers were in a bind on this one: On one hand was the information that when Marijuana alone was present in the body of someone involved in an accident, they were most often the victim. But the cacophony from police and some “Concerned citizens” groups across the country led legislators in most states to ignore science and vote stupidity.

Several studies, over the past 30 or so years, all find the same thing: People who drive after ingesting Marijuana are not significantly worse than drivers who are “Under the influence” of nothing. There are people who can smoke a lot of pot and drive without error. But there are other people who can’t.  The amount of Marijuana smoked and the amount of time it’s smoked before driving does have an effect, at least according to some studies.

Marijuana doesn’t make you something you aren’t already. If you’re a good driver without Marijuana, you’ll probably be all right. If you don’t drive well to begin with, you probably shouldn’t try to improve your skills after smoking.

The Institute for Human Psychopharmacology, the University of Maastricht in the Netherlands, performed a series of three studies including a simulator, highway driving and city driving.  According to the study:

THC’s effects on road-tracking after doses up to 300 µg/kg never exceeded alcohol’s at bacs of 0.08 g%; and, were in no way unusual compared to many medicinal drugs’ (Robbe, 1994; Robbe and O’Hanlon, 1995; O’Hanlon et al., 1995). Yet, THC’s effects differ qualitatively from many other drugs, especially alcohol. Evidence from the present and previous studies strongly suggests that alcohol encourages risky driving whereas THC encourages greater caution, at least in experiments. Another way THC seems to differ qualitatively from many other drugs is that the former’s users seem better able to compensate for its adverse effects while driving under the influence.

You can read the summary of this study at:

The Robbe study also mentioned that “Stoned” drivers tended to compensate for their perceived impairment:

“This report concerns the effects of marijuana smoking on actual driving performance. … This program of research has shown that marijuana, when taken alone, produces a moderate degree of driving impairment which is related to consumed THC dose. The impairment manifests itself mainly in the ability to maintain a lateral position on the road, but its magnitude is not exceptional in comparison with changes produced by many medicinal drugs and alcohol. Drivers under the influence of marijuana retain insight in their performance and will compensate when they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small.

Most studies that have been done show alcohol as the biggest opponent of safe driving. Marijuana is usually the second most detected psychoactive substance.  But researchers seem to have difficulty nailing down just how culpable Marijuana is as a cause of traffic accidents.

Results: Thirty-two percent (95% CI = 27-37) of the urine samples were positive for at least one potentially impairing drug. Marijuana was detected most frequently (17%), surpassing alcohol (14%). Compared with drug- and alcohol-free drivers, the odds of crash responsibility were higher in drivers testing positive for alcohol alone (odds radio [OR] = 3.2, 95% CI = 1.1-9.4) and in drivers testing positive for alcohol in combination with other drugs (OR = 3.5, 95% CI = 1.2-11.4). Marijuana alone was not associated with crash responsibility (OR = 1.1, 95% CI = 0.5-2.4). In a multivariate analysis, controlling for age, gender, seat belt use, and other confounding variables, only alcohol predicted crash responsibility.

Conclusion: Alcohol remains the dominant drug associated with injury-producing traffic crashes. Marijuana is often detected, but in the absence of alcohol, it is not associated with crash responsibility. takes you to the summary of this 2001 study published in the online professional magazine “The Journal of Trauma.”

The amount of Marijuana used does make a difference. A high dose does effect some functions such as balance, psychomotor abilities and reaction time. A Standardized Field Sobriety Test study in Australia shows the differences:

40 participants consumed cigarettes that contained either 0% THC (placebo), 1.74% THC (low dose) or 2.93% THC (high dose). For each condition, after smoking a cigarette, participants performed the SFSTs on three occasions: 5 min (Time 1), 55 min (Time 2) and 105 min (Time 3) after the smoking procedure had been completed. The results revealed that there was a positive relationship between the dose of THC administered and the number of participants classified as impaired based on the SFSTs. Results also revealed that the percentage of participants classified as impaired decreased from Time 1 to Time 3 and that the addition of a new sign, head movements or jerks (HMJ), increased the percentage of participants classified as impaired in both the low and high THC conditions. These findings suggest that impaired performance on the SFSTs is positively related to the dose of THC administered and that the inclusion of HMJ as a scored sign in the SFSTs improves their predictive validity when testing for THC intoxication.

The abstract from this study can be seen at:

Most often, in most states, motorists suspected of D-U-I-D, or “Driving Under the Influence of Drugs” are given a urine test or a blood test. If the tests show Marijuana in the person’s system, they are usually arrested.  Urine testing will not show current impairment! However, a blood test will be able to show the presence of active THC Delta 9, the primary psychoactive component of Marijuana. THC can be detected for a few hours; heavy smokers might show THC up to 24 hours. England has been working with oral swabs, with some very limited success.

Governments are grappling with how to set a limit that determines one is legally impaired. As of this writing, Colorado, a medical Marijuana state, is looking for an appropriate level. A bill making its way through that state’s legislature appears to be settling on a five Nano gram per milliliter of blood level. Some proponents think eight ng/ml presence is more realistic.

Common sense has to rule whether a person can use Marijuana and still be able to safely drive. You are responsible for your actions, regardless of whether you smoke Marijuana, drink alcohol or haven’t slept in 24 hours. The National Organization for the Reform of Marijuana Laws (NORML) has written a set of standards of personal responsibility for pot smokers. Regarding driving:

II. No Driving
The responsible cannabis consumer does not operate a motor vehicle or other dangerous machinery while impaired by cannabis, nor (like other responsible citizens) while impaired by any other substance or condition, including some medicines and fatigue.

Although cannabis is said by most experts to be safer than alcohol and many prescription drugs with motorists, responsible cannabis consumers never operate motor vehicles in an impaired condition. Public safety demands not only that impaired drivers be taken off the road, but that objective measures of impairment be developed and used, rather than chemical testing.

Some studies indicate Marijuana is, at worst, no worse than chemical prescription drugs when it comes to driving impairment. You are warned by your doctor and pharmacist when you have one of those prescriptions. Were Marijuana taxed and regulated like alcohol for personal use, or prescribed legally by a physician, there’s a better than average chance responsibility will have a chance to flourish.