Scientists with the U.S. Food and Drug Administration (FDA) are investigating whether the anti-smoking drug Chantix increases suicidal thoughts and violent behavior, the Associated Press reported on Nov. 20.

The FDA has received reports of mood disorders and erratic behavior among patients taking the drug. Chantix gained FDA approval last year to help adults trying to quit smoking, and has registered $101 million in sales.

The FDA has advised doctors to closely monitor patients who are taking Chantix for changes in behavior. According to the FDA, changes are often reported within days or weeks of taking the drug.

The drug's manufacturer, Pfizer, has added information regarding these reports to the product's label, but says that "there is no scientific evidence establishing a causal relationship between Chantix and these events." 

Pfizer said in a statement that there were no suicides in a 5,000-patient study of Chantix.