I can link you to a study that shows that marijuana effects your endocrine system in your brain and gonads. How it does that is not for me to say, but anytime you mess with someone's sexual function, you are opening up a can of worms. There are many downsides to marijuana. As an ex-marijuana user, I can attest to this fact. There are some pros, but you have to take the good with the bad as opposed to only taking the good and ignoring the bad.