Some medications that interfere with how the brain works have been found to make it more than twice as likely that a person above the age of 65 will fail a driving test.
Scientists followed almost 200 Americans who had no mental impairment for up to 10 years and gave them a driving test annually.
They found that the use of any antidepressants, including the most common selective serotonin reuptake inhibitors such as citalopram, sertraline and Prozac, was linked to a 2.8 times greater risk of failing the test.
Participants taking sedatives or hypnotics such as Xanax, or nonsteroidal anti-inflammatory drugs such as paracetamol, aspirin and ibuprofen, were about 2.7 times more likely to fail than an unmedicated person.
Individuals taking fat-lowering drugs were more likely to pass, data show, whereas there was no noticeable impact from antihistamines.
The study, conducted by Washington University, graded drivers with either a pass or fail based on official criteria and found overall that more than a third failed the test at some point.
Almost a quarter of all people were on antidepressants, data show, and three quarters of the older individuals were taking some kind of anti-inflammatory drug.
Statistical analysis, which accounted for sex, age, race, education, wealth and other factors, found that “any antidepressant use was associated with a 2.8-fold increased risk of a marginal/fail rating”, the study’s authors said.
The team also found a slightly increased risk of driving test failure for people taking sympatholytic agents, anticonvulsants and antidiabetics, but there was insufficient evidence for a definitive connection.
“The negative association between psychoactive drug use and driving performance may be explained by the effect of these drugs on neurotransmitters,” the authors said in the study, which was published in the journal JAMA Network Open.
Some antidepressants work by stopping serotonin, dopamine and other chemicals linked to happiness from being soaked up too quickly but a side-effect of this process is that they also block some receptors in the brain from receiving other signals.
“This nonselective action may lead to a number of adverse effects, including dizziness, drowsiness, attention deficit, cognitive difficulties, and psychomotor impairment,” the scientists said.
The knock-on impacts of how the antidepressants are processed in the liver could also inhibit the normal functioning of the brain, the researchers say, and therefore have a deleterious effect on driving competency.
Long-term use dangerous
The study says that there is “little impact” from anti-inflammatory drugs such as paracetamol and ibuprofen when taken in short cycles and correct dosages but the impact of long-term use in older people can be dangerous for driving.
“[Anti-inflammatory drugs] have several adverse effects, including dizziness or light-headedness, drowsiness, vision impairments, and difficulty concentrating, that can affect driving ability,” the paper said.
“This may explain the negative association observed between [anti-inflammatory] use and performance on the road test.
“Long-term use by older patients is common and could result in drug-drug interactions that exacerbate existing medical conditions known to contribute to driving impairment, such as hypertension and heart failure.”
The authors added they had found a correlation and not causation but that the findings “raise concern” about the impact common medications may have on driving competency and safety.
“Clinicians and pharmacists should be aware that patients who are prescribed these drugs could be at an increased risk of driving impairment,” the scientists advised.
“A clear discussion and review of medications in relation to the driving task should be included in the care of older adults.”