NEW YORK ( TheStreet) -- Pfizer's ( PFE - Get Report) anti-smoking drug Chantix may increase the risk of heart attacks for patients with cardiovascular disease, the Food and Drug Administration said on Thursday.

The agency cited a study of 700 people with heart disease where half of the patients took Chantix that found 2% of the Chantix users suffered non-fatal heart attacks vs. 0.9% for the placebo group. As a result of the findings, the FDA said additional safety information will be added to the Warnings and Precautions section of the drug's label.

But the FDA said in a statement: "The known benefits of Chantix should be weighed against its potential risks when deciding to use the drug in smokers with cardiovascular disease."

Pfizer's shares were at $20.12. down 0.4% during midday trading on Thursday. Year-to-date, the stock, a Dow component, is up 15%. Wall Street is bullish on the stock with 18 of the 22 analysts covering the shares at either strong buy (8) or buy (10). Revenue from Chantix totaled $199 million in the company's fiscal first quarter ended in March.

-- Written by Joe Deaux in New York.

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