A stop-smoking drug increases users' risk of a heart attack by up to 34 percent, new research suggests.
Varenicline, which is prescribed under the brand name Chantix in the US and Champix in Europe, significantly raises users' chances of being hospitalized or visiting an emergency room for a cardiovascular-related event even if it is taken for the recommended 12 weeks, a Canadian study found.
The drug is also linked to self-harm and depression in older users, the research adds.
Previous research suggests this is due to varenicline's action on receptors found in tissues throughout the body.
Varenicline increases a smoker's chances of quitting by nearly three times by reducing nicotine cravings and blocking the rewarding effects of smoking.
A 12-week course of varenicline is one of the most effective ways to help people quit smoking, according to the NHS' website.
It says the drug is safe for most people to take and does not mention its cardiovascular or neuropsychiatric side effects aside from insomnia and vivid dreams.