The Food and Drug Administration (FDA) said on Thursday that the smoking-cessation drug Chantix (vareniclene) may be associated with a small, increased risk of certain heart problems in patients with heart disease. The FDA is requiring the maker of the drug, Pfizer, to conduct a large analysis of studies to evaluate the safety of Chantix, Reuters reports.

According to an FDA statement, the risk information will be added to the “Warnings and Precautions” section of the Chantix physician labeling, and will also be included in the patient medication guide.

The FDA made its announcement after reviewing a study of 700 smokers with heart disease who were treated with either Chantix or a placebo. The study found that Chantix helped patients quit smoking for as long as one year. However, heart attacks and certain other cardiovascular events were more frequent in patients who took Chantix compared with those who took a placebo.

Since smoking is a major risk factor for heart disease, the benefits of Chantix should be weighed against its potential risks when deciding to use the drug in smokers with cardiovascular disease, the FDA advised doctors. The FDA is telling patients taking the drug to contact their health care professional if they experience new or worsening symptoms of cardiovascular disease.

Reuters notes that there is already a ‘black box’ warning for Chantix regarding psychiatric side effects such as suicidal thoughts and depression.