In March 2019 researchers from the USA published their review of the medical scientific literature to assess the effect of cannabis on male fertility. Results showed that current research supports the role cannabis may play in reducing sperm count and concentration, reducing sperm motility and viability, and causing male infertility.
Payne KS et al. Cannabis and Male Fertility: A Systematic Review. J Urol. 2019 Mar 27. [Epub ahead of print]