Drugging and Driving

2 June 2011 by David Johnson, posted in Uncategorized

ResearchBlogging.orgThere are many reasons why one might find it preferable not to drive an automobile: For one, it’s expensive (gas, insurance, repairs, and tickets). It pollutes the environment. And it’s dangerous. Based on data from the Federal Highway Administration, there are over 6 million auto accidents in the United States every year on average. And around 40, 000 of those accidents result in people being killed by people driving under the influence of alcohol.

A new review from Australian researchers provides another reason to hop on the bus or train rather than get behind the wheel. The study looked at the association between dangerous driving and taking prescription medications. And the results were not very promising, finding that users of many prescription medications are at increased risk for car accidents.

The researchers performed what is called a meta-study, in which all the research that can be located pertaining to a given topic and meeting certain criteria of validity and reliability are rolled into one mega study in an attempt to achieve maximal statistical power. Two different types of studies were examined:

1. Epidemiological studies. These are studies of patterns of association between prescription drugs and driving accidents based on real-life data coming from a variety of sources. There are several advantages and drawbacks to these kinds of studies and Wikipedia is a good place to get some background. One of the major drawbacks of epidemiological studies is that they are correlational; in other words, it’s difficult to say one thing caused another, but merely that they occurred together. One can’t control for all of the possible confounding variables that could be the true source of the relationship between variables.

2. Experimental Studies. These are controlled studies that allow researchers to explore causal relationships between variables. Again, wiki is a good place to go for a primer. The advantage of experimental studies is that if they’re designed correctly, one can explore causality but the drawback is that they lack “ecological validity”; that is, they may not represent “real world” conditions.

The over all goal of a metastudy is to ascertain whether data from numerous sources, and from both epidemiological and experimental studies, converge on the same conclusions.

Several classes of prescription drugs were examined:
1. Benzodiazepine: these include drugs such as diazepam, flurazepam, flunitrazepam and nitrazepam. They’re commonly prescribed for generalized anxiety disorder, panic disorder, Insomnia, seizures and alcohol withdrawal.
2. Non benzo hypnotics: Includes drugs like pentobarbital. These are frequently prescribed for insomnia.
3. Antidepressants, which can be divided into two classes: SSRIs and TCAs. SSRIs include drugs like Lexapro, Prozac, and Celexa. TCAs, or trycylic antidepressants, include drugs like mipramine (Tofranil) and maprotiline (Ludiomil).
4. Anxiolytics (Anti Anxiety drugs)
5. Opioids

For those interested in the details, please consult the study. I’ll just be presenting a simplified summary of the findings. But before I get there, just a couple of quick thoughts. Meta studies can often be difficult to interpret. Particularly for a topic such as this, where there are so many confounding variables, such as a huge variety of different types of drug, varying range of dose, the problem that those on medication also have depression, anxiety, and other disorders (making it difficult to parse out the effects of the drug alone), tolerance effects, age and gender effects, the possibility that the epidemiological studies only include the worst cases (only accidents that resulted in injury), and so on. It becomes very difficult to make conclusive or generalizable statements about the findings. Some researchers are opposed to meta studies for that very reason. That being said, the evidence here does seem to have reasonably converged toward a handful of conclusions. Keeping the limitations in mind, here they are:

1. Benzodiazepine users show 60-80% increased risk of traffic accidents. Drivers responsible for causing an accident are 40% more likely to be positive for benzos than those who are not responsible. Elderly users of benzodiaepines show decreased risk (versus non-elderly).

2. Benzodiazepine plus alcohol users show 7.7 fold increase in risk for traffic accidents

The 2- to 3-fold increase in accident risk associated with … long-acting benzodiazepines and zopiclone is equivalent to what has been observed with a blood alcohol concentration of 0.05-0.08 g/dL,[100,101] which is above the legal limits for driving in most countries…

The authors recommend that anyone prescribed diazepam should be urged not to drive for the first four weeks of treatment.

3. Anxiolytics seems to impair drivers independent of the drug’s half life. (A half life is the duration of action of a drug and indicates the period of time required for the drug in the body to be reduced in half.)

4. Impairment caused by hypnotics tends to be related to the drug’s half life.

For hypnotic medication, an option for prescribers is to avoid these hypnotics (flurazepam, flunitrazepam, nitrazepam and zopiclone) if patients are engaged in driving. Relatively safer alternatives would be shorter acting hypnotics, such as triazolam, temazepam, zolpidem and zaleplon, which were not found to cause driving impairment, at least in experimental studies (although there is evidence that some of the drugs are associated with increased accident risk)…

5. As far as antidepressants go, no clear distinction emerged between sedative and non-sedative subclasses (according to epidemiological studies). One major confounding variable in the studies examined is depression itself, as cognitive and psychomotor deficits are associated with depression alone. Furthermore, antidepressants might interact differently depending on stage of treatment, e.g. effects of antidepressants take one to two weeks to appear, so driving may be even more impaired over this time period than depression alone or after drug effects kick in.

Sedative antidepressants probably lead to worse driving for the first 3-4 weeks, and until tolerance to sedative effects increases and depression lifts. This is supported by some experimental evidence. (Patient groups with sedative/non-sedative antidepressants improved their driving skills after a few weeks). Epidemiological studies suffer from the confound of comparing groups on anti-depressants (people with depression) with those not on anti-depressants (people who don’t have depression) and are therefore of limited utility.

6. Opioids – There weren’t enough studies of opioids and driving to make any conclusions.

I wasn’t able to locate data indicating how many people in the US are currently taking the drugs mentioned in this study. What I did find was that antidepressants (many of which are probably sedatives) are the most popular prescription drug for adults aged 20 to 59 in the US. And the most recent annual data (from the CDC) suggests that 48% of Americans took at least one prescription drug in the past month. This suggests the possibility that the number of those driving under the influence of cognitively-impairing prescription drugs is likely to be in the millions country wide. Cause for concern? Perhaps. Prescription drugs are certainly not becoming any less popular, and I’m certainly glad to live in a city that provides alternative transportation options. Then again I often bike in that city, and mildly sedated depressive or anxious drivers might be the least of my worries (cab drivers and delivery trucks being a much larger concern).

Dassanayake T, Michie P, Carter G, & Jones A (2011). Effects of benzodiazepines, antidepressants and opioids on driving: a systematic review and meta-analysis of epidemiological and experimental evidence. Drug safety : an international journal of medical toxicology and drug experience, 34 (2), 125-56 PMID: 21247221

4 Responses to “Drugging and Driving”

  1. Laura Wheeler Reply | Permalink

    Hi Dave what a thoroughly well researched post. 

    Dangerous driving seems to be a common theme on NN, have you seen Muka’s blog post, talking while driving.

    I think the points you have made have raised an intriguing and somewhat controversial question, should people on these types of medication be banned from driving?

    I have to say, my answer is yes – especially if the science shows that it can affect your abilities to drive safely.  What do other people think?

    My mother was recently in a really bad car accident where a 98 (yes!) year old man drove into her on a roundabout.  There were several whiteness, thankfully, who all said the same thing, that the old man was not concentrating and drove into her without looking. So that leads me to my question, from a neuroscientist’s perspective, I wonder if age is also an issue that may influence your ability to drive?  (I shall not go into gender issues here…)

  2. Jarred Yacob Reply | Permalink

    The age question is very interesting. I’m sure that as people age and lose some mental sharpness they become worse drivers. However, the rate at which everyone’s mental sharpness goes away is very different. So its impossible to say that anyone over 90 shouldn’t be allowed to drive. But I wonder if there could be a mental alertness test or something that could be used for assesment before a license is reissued.


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  3. Laura Wheeler Reply | Permalink

    Jarred, I think the a mental alertness test would be a great idea!! Or possibly it should be compulsory to re-take your driving test every 20 years, that could solve this issue?

  4. Austin Seofirm Reply | Permalink

    There are a lot of things that can degrade driving performance — drugs (including alcohol), health, physical impairments, fatigue and emotional state to name a few.  It’s difficult to imagine legislation or regulations that would effectively cover all of these causal factors; and the implementation of these restrictions would be rediculoulsy unworkable.

    I like Laura’s suggestion of periodic driver testing (although every 5 years might be better), and there are a couple more less intrusive ways to address this issue:

    1) Require physicians to report more categories of impairment to the state DOTs.  MDs are currently required to report mental impairment or drug abuse (and most DOTs suspend licenses for these); this should be expanded to include other driving impairments.

    2) Driver education, PSAs and social marketing campaigns should remind us that a fair percentage of the other drivers on the road are drunk, drug-impaired, vision-impaired, tired, angry and/or depressed, and we need to be alert for unexpected driving behavior.




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