New York : Contrary to popular perception, smoking cessation drugs do not increase the risk of serious neuropsychiatric adverse effects such as depression, hostility or suicidal behaviour, says a large study.

Researchers have found that compared to the nicotine patch and a placebo the smoking cessation drugs varenicline and bupropion do not show a significant increase in neuropsychiatric adverse events.

“There are one billion smokers in the world and nearly six million smoking-related deaths each year, but there are only three approved medication treatments for quitting: nicotine replacement therapies like the patch and the two non-nicotine medications, bupropion and varenicline,” said first author of the study Robert Anthenelli, professor at the University of California San Diego School of Medicine.

The study, published online in the journal The Lancet, is important because it prospectively examined the neuropsychiatric safety risks and quit-enhancing potential of the three medication classes versus placebo in a rigorous, adequately-sized, randomised controlled trial, Anthenelli said.

The researchers sought to directly assess the safety and efficacy of varenicline and bupropion compared to the nicotine patch and to a placebo in smokers with and without psychiatric disorders.

The study involved examination of more than 8,000 smokers seeking to quit in 16 countries over a period from November 2011 to January 2015.

Trial participants, investigators and research personnel were blinded to who received which treatment.

In terms of safety, approximately two percent of non-psychiatric participants reported moderate or severe adverse neuropsychiatric events for any of the treatments.

In the cohort of participants with psychiatric disorders, moderate and severe adverse neuropsychiatric events were slightly higher across the board: 6.5 percent for varenicline, 6.7 percent for bupropion, 5.3 percent for the nicotine patch and 4.9 percent for placebo.

Anthenelli said the risk difference in the incidence of serious neuropsychiatric adverse events for varenicline and bupropion was not significantly higher than placebo – but that psychiatric patients trying to stop smoking are likely to have more confounding factors in treatment and appear to have a harder time quitting.