This article in Scientific American is rather complex reading but reveals some important findings. One of the items in the piece, about study results just published in the journal Cell, is tucked in at the very end -- which is too bad, because it's a tidbit of data that even the least technical reader can grasp.
According to researcher Yurij Kirichok of the University of California at San Francisco, "Marijuana likely activates sperm prematurely, leaving them burnt out in a matter of hours."
Importantly, this study was not about marijuana's effects on male fertility. Rather, the researchers were investigating molecular components that impact how and when a sperm cell gets moving. Besides pinpointing a molecule (Hv1) that activates a resting sperm cell, they also found a few more pieces to the puzzle linking marijuana and male infertility, via endocabbinoids.
Too much medical geek talk? Just simplify it to what we typically recommend: avoiding toxins of all kinds can enhance fertility.