The MHRA has received 118 reports of suicidal ideation among patients since the drug was launched in December 2006.
There has also been two suicides, four suicide attempts, four incidents of suicidal behaviour and five incidents of suicidal depression reported.
Most of the patients had pre-existing psychiatric conditions – but there were some suicide-related events among patients with no known pre-existing psychiatric conditions and in patients who continued to smoke.
The MHRA said: ‘Anyone taking varenicline who develops depression or suicidal thoughts should stop their treatment and contact their doctor immediately.’
The drug is produced by Pfizer under the brand name Champix, with a 56-tab pack costing £54.60.