Can smoking marijuana make a guy grow breasts? A: Yes it can if a guy smokes a lot of it. Heavy use of marijuana can “turn off” the brain hormones that tell the testicles to make testosterone (male sex hormone). When this happens there may be enough natural estrogen (female hormones) present to stimulate breast tissue. Other related side effects of very heavy marijuana use may include decreased size of testicles, loss of interest in sex, difficulty maintaining an erection and difficulty growing muscle. I don’t know of any scientific data that has determined how much marijuana use is enough to cause breast growth. It may also vary with individuals. Avoidance is safest. http://www.teengrowth.com/index.cfm?action=info_advice&ID_Advice=3050 What kind of obvious bullshit are they trying to pull on us. I'm horny as hell when I'm stoned and I prefer working out when stoned. And my testicles have not shrinked since I started smoking. They really have run out of ideas to scare people.