Anti-smoking drugs do not elevate risk of serious neuropsychiatric adverse effects

Compared to the nicotine patch and a placebo, the smoking cessation aids varenicline (marketed as Chantix in the US) and bupropion (Zyban) do not show a significant increase in neuropsychiatric adverse events, reports an international team of researchers in a study published online April 22 in the journal The Lancet.

"There are 1 billion smokers in the world and nearly 6 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 Robert Anthenelli, MD, professor of psychiatry, director of the Pacific Treatment and Research Center at UC San Diego School of Medicine and first author of the study.

Anthenelli said the so-called EAGLES study 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, randomized controlled trial.

It is the result of a Food and Drug Administration (FDA) mandate following post-marketing reports suggesting varenicline and bupropion might cause adverse neuropsychiatric events, such as increased agitation, depression, hostility or suicidal behavior.

The FDA requested that both medications carry boxed warnings in their labeling. This has resulted in limitation in use. The EAGLES study was funded by Pfizer and GlaxoSmithKline, makers of varenicline and bupropion, respectively, and designed in consultation with the FDA.

Authors 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. It involved a randomised, controlled, double-blind trial examining 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.

"This is the first study to compare the safety and efficacy of the three first-line smoking cessation aids on the market, head-to-head, in smokers. It's the largest double-blind smoking cessation medication trial to date," said Anthenelli. "And no study has done so in smokers with current or past psychiatric disorders who consume roughly 45 percent of the cigarettes sold in the U.S."

In terms of safety, approximately 2 per cent of non-psychiatric participants reported moderate or severe adverse neuropsychiatric events for any of the treatments. Specifically, 1.3 per cent for varenicline, 2.2 per cent for bupropion, 2.5 per cent for the nicotine patch and 2.4 per cent for placebo.

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

The efficacy or success rate, measured as biochemically-confirmed continuous abstinence for weeks nine to 12 after treatment began, was broadly consistent with past research and predictions.

Regardless of participants' psychiatric status, varenicline was found to be more effective at helping smokers achieve abstinence than bupropion, the patch or placebo; bupropion and patch were more effective than the placebo. Across all cohorts, the most frequent adverse events were nausea, insomnia, abnormal dreams and headache.