European regulators are following in the footsteps of their US counterparts and are looking into reports of suicidal thoughts and aggressive and erratic behaviour in patients who have taken Pfizer’s smoking cessation product Chantix.

The European Medicines Agency said that new warnings for doctors and patients were needed to increase awareness of cases of suicidal thoughts linked to Champix (varenicline) and has asked Pfizer to respond by December 19.

The New York-based drugs giant said that it was working closely with European regulators to review case histories but it also noted that there is no scientific evidence of a causal relationship between Champix, sold as Chantix in the USA, and reported events. The review is still ongoing but Pfizer said that “clinicians should be aware of the possible emergence of depressive symptoms in patients undergoing a smoking cessation attempt, with or without treatment, and should advise patients accordingly".

The news comes in the wake of reports last month from an ongoing safety review carried out the US Food and Drug Administration using post-marketing data submitted by Pfizer. The agency said that “a preliminary assessment reveals that many of the cases reflect new-onset of depressed mood, suicidal ideation, and changes in emotion and behaviour within days to weeks of initiating Chantix treatment”.

Champix has proved to be a successful drug for Pfizer since its launch in August last year and had sales of $241 million in the third quarter.