The most effective prescription drug used to quit smoking initially helps women more than men, according to a study led by Woman’s Health Research at Yale Deputy Director Sherry McKee.

The study, published Wednesday by the journal Nicotine and Tobacco Research, found that varenicline, marketed as Chantix, was more effective earlier in women, and equally effective in women and men after one year.

“Studies show that women have a harder time quitting smoking than men, even as quitting has shown greater benefits to women’s cardiovascular and respiratory health,” said Dr. Sherry McKee, professor of psychiatry and lead researcher of Yale’s Specialized Center of Research focused on gender and tobacco dependence. “With this first comprehensive analysis of sex differences in the effectiveness of this drug, now women and their healthcare providers can better decide how to successfully quit and live longer, healthier lives.”

Tobacco use is the leading preventable cause of sickness and death in the United States, killing 556,000 every year and costing $96 billion in medical expenses and $97 billion in lost productivity.

McKee’s team found that varenicline was 46% more effective in women after three months of treatment, and 31% more effective at maintaining complete abstinence after six months.

Analyzing clinical trial data from 6,710 smokers using varenicline for smoking cessation through Dec. 31, 2014, McKee’s team confirmed many prior clinical trial findings in demonstrating that women were less likely than men to quit when using a placebo.

Unlike nicotine replacement or bupropion (marketed as Wellbutrin and Zyban, among other brand names), which produce lower rates of quitting in women, varenicline produced similar rates of smoking abstinence for men and women — 53% after three months, according to the researchers. But when factoring in the lower placebo effect in women, they found that varenicline increased the odds of women quitting by 46%.

“While it’s clear that sex differences in varenicline efficacy exist, we don’t yet know why varenicline is particularly effective for women,” McKee said, adding that sex differences in the nicotine receptor system in the brain may be a key factor.

“This is the first demonstration that women compared to men have a preferred therapeutic response for a smoking cessation medication when considering short-term treatment outcomes and equal outcomes at one year,” she said. “Varenicline appears to be particularly useful for reducing the sex disparity in smoking cessation rates.”

Other authors on the study included Dr. Philip H. Smith of Yale School of Medicine; Women’s Health Research at Yale Director Carolyn M. Mazure, Ph.D.; Dr. Andrea H. Weinberger of Yeshiva University, and Mira Kaufman of Brown University.

The study was supported by grants from the National Institutes of Health Office of Research on Women’s Health and the National Institute of Drug Abuse.

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For questions, please contact Rick Harrison, Communications Officer, at 203-764-6610 or rick.harrison@yale.edu.