There 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 its 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 study 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 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 meta-study is to ascertain whether the 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: Include 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)
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 people 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
Google, are you reading my mind?
One interesting aspect of having a blog is checking out the search terms that people used to land at one’s site. It’s often difficult to figure out why a particular and seemingly unrelated term might bring someone this way.
But one recent search seems to have transcended the blog and gone straight into my brain-o-sphere, into the existential recess where some of my darker thoughts about grad school are stored:
Google, you know me so well. Now stop it, you’re freaking me out.
In a paper recently published in the journal Drug and Alcohol Dependence, Danish researchers attempted to establish standard mortality ratios for the drugs cannabis, cocaine, amphetamine, MDMA (ecstasy) and opioids (e.g. heroin)*, while taking into consideration the effects of two intervening variables: drug injection with needles and psychiatric disorders (Is the mortality rate of cocaine users mediated by whether they have, for example, clinical depression?)
(*Individuals’ primary drug of choice)
The population they looked at included 20,581 people treated for drug abuse in Denmark over a 10-year period from 1996-2006. (These data are correlational and, therefore, the possibility of unidentified moderating variables exerting an effect on death rates is high.)
In brief, the results showed the following:
1. Those who injected drugs showed significantly higher mortality rates across the board. (This does conflict with past findings, which found no difference.)
2. Overall, psychiatric illness was not associated with higher mortality rates, with the exception of cocaine/amphetamine users, who, if they presented with psychiatric disorders, did show higher morality rates.
3. Pot smokers showed 5x increase in mortality rates (compared to the general population). Researchers suggest that increased mortality among pot smokers could be related to driving accidents, violent injuries and various other types of accidents. (a personal note: Based on my personal experience, this seems unlikely. Pot smokers tend to drive very conservatively (too slow, if anything!) and are famously not prone to violence.) What seems more likely to explain pot smokers’ higher mortality rate is that they are also using other drugs. Other studies have borne this out.
4. Cocaine and amphetamine users showed 6x death rates of the general population. Previous reports on stimulant abuse related deaths are highly variable. The variability is likely the result of other factors including physical conditions, HIV/AIDS, overdose, cardiovascular problems, injuries accidents, violent deaths and suicides.
5. Opiod users show increased mortality rates. Findings for both stimulants and opioids are in accordance with studies from other countries. Users of Heroin and other opioids showed by far the highest mortality rates of all drugs of abuse.
6. Ecstasy (MDMA) users did not show increased mortality rates. (However, it’s possible that a low number of deaths from MDMA contribute to low statistical power).
Conclusions that can be drawn from this report? Stay away from all drugs if you want to increase your chances of staying alive; but, especially, don’t do intravenous heroin. Psychiatric disorders plus drugs of abuse aren’t associated with increased mortality risks except for in the case of cocaine/amphetamine. Ecstasy is unlikely to kill you on its own, but that’s not to say it won’t do some long-term damage if abused. Although marijuana users showed higher mortality rates, there’s not good reason to believe this is solely the effect of marijuana, but other factors. Finally, the population under study here consisted of people seeking treatment, so it’s unknown if this represents the drug using population as a whole.
I think it’s pretty clear, given the number of questions and unknowns this study presents, that there is a lot more to learn about drug-related mortality risk.
Arendt M, Munk-Jørgensen P, Sher L, & Jensen SO (2011). Mortality among individuals with cannabis, cocaine, amphetamine, MDMA, and opioid use disorders: a nationwide follow-up study of Danish substance users in treatment. Drug and alcohol dependence, 114 (2-3), 134-9 PMID: 20971585