A newer smoking cessation drug is not linked to an increased risk of self-harm or depression, a British study suggests.

Health Canada and the U.S. Food and Drug Administration have warned that people taking varenicline — sold in Canada as Champix and in the U.S. as Chantix — have experienced unusual feelings of agitation, depressed mood, hostility, changes in behaviour or impulsive or disturbing thoughts, such as ideas of self-harm or of harming others.

The smoking cessation product is effective. British researchers writing in Friday's issue of the British Medical Journal looked for more evidence of adverse neuropsychiatric effects related to the drug.

The team analyzed information on 80,660 men and women, aged 18 to 95, who were prescribed a smoking cessation product between September 2006 and May 2008.

Complaints received in Canada

No clear evidence was found linking varenicline or bupropion to increased risk for self-harm, suicidal thoughts or depression, the researchers said.

"Although a twofold increased risk of self-harm with varenicline cannot be ruled out, these findings provide some reassurance concerning its association with suicidal behaviour," the study's authors concluded.

Among the study participants were prescribed smoking cessation products:

• 10,973 to varenicline.
• 6,422 to bupropion.
• 63,265 to nicotine replacement therapy such as the patch, inhaler, gum, tablet or lozenge.

All electronic patient records over the period of the prescription and for three months after the date of the last prescription were examined for incidences of fatal and non-fatal self-harm, suicidal thoughts and depression.

The researchers recommended further study of varenicline's effect on suicide risk in other databases and adverse event reports in clinical trials.

Any risks associated with varenicline must be balanced the long-term benefits of butting out and the drug's effectiveness as a smoking cessation product, they added.

Champix has been approved since April 2007. Of the 818 complaints about Champix Health Canada had received complaints on its adverse reaction database, 520 involved psychiatric problems, CBC News reported in February.

From January to November 2008, nearly 1.1 million Champix prescriptions were dispensed from Canadian retail pharmacies, according to IMS Health Canada, which tracks the pharmaceutical industry.

The study was funded by Britain's Medicines and Health Regulatory Agency.