The smoking cessation medication Chantix is being tested as a possible treatment for addiction to alcohol, cocaine and methamphetamine. The drug’s package insert includes prominent warnings about possible “serious adverse events” including changes in behavior, hostility, agitation, depressed mood, and suicidal thoughts or actions. According to The Philadelphia Inquirer, people with substance use disorders may be especially vulnerable to such problems.

Researchers at the University of Pennsylvania, the University of California, Los Angeles (UCLA), and other medical centers, as well as the National Institute on Alcohol Abuse and Alcoholism, are testing the drug as a treatment for various substance addictions, the article notes.

The studies on Chantix are excluding people with suicidal tendencies, or mental illnesses such as bipolar disorder. So far, researchers of about a dozen studies have not seen any major psychiatric events in patients taking Chantix.

One study found that among cocaine users, Chantix was no more effective than a placebo, while another study found it was more effective compared with a placebo. Studies that are looking at Chantix to treat alcohol abuse also have produced conflicting results. A small UCLA study has found that Chantix reduces meth use. The Mayo Clinic is testing the drug in smokers who drink heavily to see whether it can reduce use of both substances.

In October, the Food and Drug Administration said Chantix is no more likely than nicotine patches to cause psychiatric events that require hospitalization.

The FDA drew its conclusions after reviewing two studies comparing Chantix to nicotine replacement therapy, including nicotine patches. The agency acknowledged the studies had limitations and will keep the “black box” warning labels on Chantix to advise about possible psychiatric side effects.

The manufacturer of Chantix, Pfizer, is conducting a large safety clinical trial of the drug to assess psychiatric side effects. Results are expected in 2017.