The pills are known to cause drowsiness, although at this point it is not known if Jenpop Weeraporn, the driver of the Mercedes, had taken one before driving.

However, Jenpop does have a record of seeking treatment for depression and this would not be the first time that motorists with symptoms of mental illness have been involved in fatal accidents.

Nine years ago, Kanpitak “Mu Ham” Pachimsawat, the son of former Miss Thailand Sawinee Pachimsawat, slammed his Mercedes-Benz into people standing at a bus stop, killing two and injuring 10.

After running them over, Kanpitak got out of his car to argue with a bus driver who had allegedly cut in front of him. The suspect’s father later defended his son, saying he had psychiatric symptoms and was being treated at the Galaya Rajanagarindra Institute.

Then on March 7, a video clip went viral showing a white car going against the traffic and crashing into a taxi on Lat Phrao Road. A naked woman emerged from the car and began walking up and down the road until passers-by tried to cover her up. Police later learned that the woman suffered from bipolar syndrome.

With so many similar cases, road-safety expert Raksit Thitipattanapong has come to believe that accidents are not just caused by recklessness and the violation of traffic laws, but also by drivers who are unable to control their emotions like normal people. Hence, he said, the Land Transport Department should step up measures to have drivers undergo physical and psychiatric examinations before issuing or renewing driving licences.

There should also be exams for elderly people who might not be physically fit to control a car, he added.

“I have urged the Land Transport Department many times to come up with these measures because if people with mental and physical problems are allowed to drive, they risk causing accidents, especially drivers with mental disorders. They cannot make decisions like normal people,” he said.

Deputy Bangkok police chief Pol Maj-General Adul Narongsak supported Raksit’s idea, saying that revoking the driving licences of mentally ill people after they caused an accident was not really solving the problem. “This problem will continue if it is not addressed at the root,” he said.

“Police can only address the problem after it occurs. The Land Transport Department can solve the problem before it occurs. Getting a driving licence in Singapore and the United States is very difficult. Here, you apply in the morning and get it in the afternoon,” he said.

He added that it was time for Thailand to meet international standards and make mental examinations mandatory for driving licence applicants.

“If physicians give a person a clean bill of health and later they are found to have caused an accident due to mental illness, then the physician should be held responsible,” Adul said.

Land Transport Department deputy director general Nanthapong Cherdchu, meanwhile, insisted that it was mandatory for people to submit a medical certificate when applying for or renewing a licence. The certificate has to guarantee that applicants do not suffer from a disease that can pose a threat on the road, and that they do not have Elephantiasis, tuberculosis or muscular atrophy.

Before being granted licences, motorists have to undergo physical fitness and vision tests. Those seeking to renew their licences also have to submit a medical certificate that is less than a month old.

A psychiatric test is not yet required as the Land Transport Department feels it might become an extra burden for motorists. The department, however, has met with the Medical Council and discussed the option of adding mental illnesses to the medical certificate. If a physician finds a motorist is mentally ill, his or her driving licence would be revoked for a year. However, the plan has not yet been implemented.

Nanthapong said motorists who applied for a licence or a renewal might not be ill at the time of the application, but might develop symptoms due to stress, drug abuse or alcohol. “These reasons could be behind weariness or drunk driving,” he said, adding that given repeated accidents, state agencies were moving to amend traffic laws and tighten regulations on granting driving licences.