European regulators cleared an antismoking pill made by drug giant

Pfizer

(PFE) - Get Report

about four months after it was given the green light in the U.S.

The approval of the drug, called Champix in Europe, was based on clinical trials involving 4,000 smokers who smoked an average of 21 cigarettes a day for an average of 25 years.

Patients who received a 12-week course of the drug were twice as likely to quit smoking as patients taking the antidepressant bupropion, which goes by the

GlaxoSmithKline

(GSK) - Get Report

brand name Wellbutrin. Patients taking Champix were nearly four times more likely to quit compared with those given a placebo.

The most common side effects of Champix were nausea, abnormal dreams, headache, insomnia, constipation, gas and vomiting, but the company says the drug was generally well tolerated in trials. The rate at which patients opted to discontinue treatment with the drug was 11.4%, compared with 9.7% of patients on the placebo.

Champix was approved by the Food and Drug Administration for smoking cessation in May under the brand name Chantix.