It turns out that taking SSRIs like Paxil can increase DNA fragmentation in sperm. This is according to research presented recently at the 64th annual meeting of the American Society for Reproductive Medicine in San Francisco.

While the research wasn’t aimed directly at the study of male fertility, it did reveal that SSRIs caused men to be five times more likely to develop abnormal sperm DNA. The results, which have been called “troubling,” suggest an adverse effect on fertility, according to co-investigator Dr. Cigdem Tanrikut from Harvard Medical School in Boston.

She said that during the clinical trial, “the first study to assess the impact of an SSRI on semen parameters in healthy men,” 35 participants had taken Paxil for 5 weeks. They took 10 mg once a day the first week, 20 mg for the second, 30 mg for both the third and fourth weeks and then back to 20 mg the fifth week.

They tested the semen samples that were taken before the men began taking the Paxil and then again after four weeks of taking the drug. The tests revealed that the average DNA fragmentation score rose from 13.8 percent before the Paxil to 30.3 percent after four weeks. The study also showed that the number of men that showed a fragmentation score of 30 percent or more before they started treatment increased from 10 percent to 50 percent.

As to how the Paxil affects the semen directly, it seems to slow down the sperm when it is traveling through the body. In some cases, the sperm was so slow that there was practically no sperm at all in the ejaculate. Having discovered this side effect of Paxil, more studies likely will be conducted to further verify these claims.