Men who smoke marijuana frequently have significantly less seminal fluid, a lower total sperm count and their sperm behave abnormally, research shows. Does weed lower sperm count? Marijuana is an illegal drug that comes from Cannabis sativa, a hemp plant. It is probably the most commonly used illegal. Cannabis is a drug of abuse also known as grass, hashish, hemp, Chronic use can lower sperm count in males and lead to irregular periods in females.