Health Canada says it is in the process of strengthening safety information on the labels of the smoking-cessation product Champix.

In a statement Tuesday, it said it's working with the drugmaker Pfizer to update prescribing information after reports of serious psychiatric symptoms associated with the use of Champix.

Health Canada says label changes that increase awareness of the risk will be passed along to consumers and medical professionals when they are finalized.

Champix can be an effective tool for quitting smoking, it says, but there have been reports in some patients of unusual feelings of agitation, depressed mood, hostility, changes in behaviour, or impulsive or disturbing thoughts such as thoughts of self-harm or harm to others.

Health Canada says people taking the drug and their families are reminded to be aware of any unusual thoughts, feelings or behaviours, especially those related to depression, aggression or self-harm.

It isn't clear whether Champix is the cause of these psychiatric symptoms, but patients should stop the drug immediately if there are such concerns.

And patients should avoid driving or operating machinery until they're sure that Champix doesn't have an adverse effect on them, Health Canada said.

In issuing its reminder Tuesday, the federal agency noted that it's a time of year when many smokers are attempting to kick the habit.

In Montreal, Pfizer spokesman Christian Marcoux said that Champix is "safe and very efficacious" and that some symptoms are actually caused by the act of quitting smoking.

"Any individual attempting to quit smoking should be monitored and work with their physician because smoking cessation will generate or exacerbate such symptoms, with or without medication," he said.

He said the simple fact of quitting smoking will trigger behavioural changes.

"Smoking is a very nasty addiction and it's quite a challenge to work on that addiction," he said.