Government scientists are investigating whether a drug used to help people quit smoking also increases suicidal thoughts and violent behavior.
The Food and Drug Administration says it has received reports of mood disorders and erratic behavior among patients taking Pfizer's prescription drug Chantix.
The FDA says it is still gathering information about the drug. But officials are advising doctors to closely monitor patients taking Chantix for behavior changes.
Regulators are unclear if the drug is directly responsible for abnormal behavior, because nicotine withdrawal often aggravates existing mental problems.