Researchers at the U of C and two other universities have discovered that a drug used to treat alcohol and heroin addicts could also help women stop smoking, according to a study published in the October 2006 issue of Nicotine and Tobacco Research.

The team studied the effects of the opiate blocker naltrexone on smoking cessation in men and women.

All volunteers received nicotine patches for a month after quitting, as well as weekly behavioral counseling from two weeks before quitting until four weeks afterward. In addition, half of the participants received 50 milligrams per day of naltrexone from three days before quitting to eight weeks afterward; the other half received a placebo.

After eight weeks of treatment, men and women who received naltrexone fared roughly equally: 62 percent of men and 58 percent of women successfully quit as defined by the study. Among those who received the placebo, however, there was a marked difference: Success rates were 67 percent for men but a mere 39 percent for women.

The researchers are not sure exactly how naltrexone helped some women quit smoking, although they think it’s related to the drug’s function as an opioid blocker. It inhibits the pleasurable signals in the brain that are emitted when people use drugs like nicotine or alcohol.

“[Naltrexone] theoretically may block the endorphin-like positive effects of smoking,” said Andrea King, an associate professor of psychology at the University and one of the study’s authors, in an e-mail interview.

The team cannot explain exactly why naltrexone works for women but not for men, although they have several theories. Hormonal and genetic differences between the sexes may contribute to the drug’s gendered success rate. It may also be that women smoke for more complex reasons than men and have a tougher time quitting on a standard regimen. In addition, naltrexone seemed to ease the symptoms of nicotine withdrawal in women, including sad mood, difficulty concentrating, and irritability.

“These negative effect–type symptoms were reduced by naltrexone in women. For men, they were decreased similarly with naltrexone or placebo,” King said.

Finally, the drug’s effects on weight gain after quitting may also play a role. Subjects who received the placebo gained an average of four pounds in the first month after they quit. In the naltrexone group this amount was reduced to one pound. “Women are more sensitive to smoking-related weight gain than men,” so this might account for the drug’s differential effects, King said.

King now plans to conduct a larger and longer smoking cessation study to examine the effects of naltrexone more carefully.

The study was authored by King, and included additional U of C contributors Harriet de Wit and Rosslynn C. Riley in the Department of Psychiatry and Dingcai Cao of the Department of Health Studies, along with Brown University’s Raymond Niaura and University of Minnesota’s Dorothy Hatsukami.