Treatment for opioid addiction tampers with the testosterone levels of male but not female opioid users, McMaster research has shown.

In a paper published Tuesday in the journal Scientific Reports, the researchers say addiction treatment may need to change to address the side-effect.

The study found men using methadone, which is used for opioid addiction treatment, have significantly suppressed testosterone levels of about a quarter of the testosterone of men not using opioids. In women using methadone for addiction treatment, testosterone levels were not significantly impacted, even considering the menstrual cycle.

Low testosterone in men has been associated with poor quality of life as well as erectile dysfunction, fatigue, and mood disturbances.

“We expect that treating testosterone deficiency will improve outcomes of methadone treatment for patients, including treatment response and retention,” said Dr. Zena Samaan, principal investigator of the study.

“Doctors should also ensure the patients are being prescribed the lowest dose of opioids including methadone for effective treatment to minimize testosterone suppression.”

She added that this is a particular issue in Canada, the second largest consumer of opioids in the world.

Dr. Samaan is an associate professor of the psychiatry and behavioural neurosciences department of McMaster’s Michael G. DeGroote School of Medicine.

The study involved information from 231 patients with opioid dependence receiving methadone in Ontario, as well as 783 Ontarians not using opioids. It was funded by the Drug Safety and Effectiveness Network of the Canadian Institutes of Health Research and the McMaster Department of Psychiatry and Behavioural Neurosciences.

The study was conducted by the Population Genomics Program of McMaster’s Chanchlani Research Centre, and Ontario Addiction Treatment Centres.