Taking happy pills before driving makes you more prone to accidents, researchers claim.
They have found that taking common antidepressants such as Prozac and Seroxat heightens the risk by 70 per cent.
Even patients who have only been on the pills for a few hours are far more likely to have a crash if they get behind the wheel.
Although some manufacturers put warning notices on boxes telling patients their judgment may be impaired, they don’t specifically tell them not to drive.
But it is now thought that the same chemical changes that improve mood among those who take the pills also slows down reaction times.
Researchers say the study shows that doctors should be banning patients from getting behind the wheel as soon as they put them on a course of drugs.
Recently the number prescriptions for antidepressants have soared and last year nearly 50 million were handed out, a rise of a quarter in four years.
Campaigners have blamed the economic woes but also say GPs have become better at diagnosing the illness so are more likely to hand out the pills.
Researchers from the University of Taiwan looked at data on 36,000 and compared the likelihood of them having an accident to whether they were on antidepressants.
They also looked at other drugs including sleeping pills and antipsychotics which are taken for mental illnesses as well as dementia.
Collectively all of these drugs are known as psychotropic medication which means they affect mental activity or behaviour.
Those taking a common group of antidepressants known as selective serotonin reuptake inhibitors (SSRIs) which include Prozac and Seroxat were 72 per cent more at risk.
Even patients who had only started the course of drugs that day were 74 per cent more likely to have an accident within 24 hours than those not on medication.
Those on a type of sleeping pills called benzodiazepines were 56 per cent more at risk of accidents while antipsychotics increased the likelihood by just 9 per cent.
Lead researcher Hui-Ju Tsai, who is based at the National Health Research Institutes in Zhunan, Taiwan, said: ‘ Our findings underscore that people taking these psychotropic drugs should pay increased attention to their driving performance in order to prevent motor vehicle accidents.
‘Doctors and pharmacists should choose safer treatments, provide their patients with accurate information and consider advising them not to drive while taking certain psychotropic medications.’