The finding, published in the journal Human Reproduction on Feb. 5, contradicts all conventional knowledge on how weed affects sperm. Analysis of 1,143 semen samples from 662 men collected between 2000 and 2017 at the Fertility Clinic at Massachusetts General Hospital showed that those who had smoked weed at some point in their life had a mean sperm concentration of 62.7 million sperm per milliliter (mL) of ejaculate, while men who’d avoided marijuana entirely had mean concentrations of 45.4 million/mL.Not only that, but only 5% of weed smokers had sperm concentrations below the 15 million/mL threshold the World Health Organization has set for a “normal” sperm count, versus 12% of men who’d never smoked marijuana.
The Harvard T.H. Chan School of Public Health researchers wrote in their paper that they expected marijuana use to be associated with lower sperm count; previous research has shown this, but such studies have typically focused on men with drug abuse history.
By contrast, the recent paper simply asked men if they’d smoked more than two joints in their life. Slightly more than half, 55%, said they’d tried two or more marijuana joints at some point, while the rest said they had not—though, note the researchers, some may have denied trying the drug due to its illegal status.The study is imperfect in other ways. For example, the participants are not necessarily representative of the general population. They were predominantly white, college educated, have a mean age of 36, and were all seeking treatment at a fertility center. But though further research is needed to corroborate the findings, the authors have a couple of theories about why weed could correlate with higher sperm count.