They also found that the sperm concentrations which is measured slightly differently than sperm count were 28 percent lower in the men who smoked marijuana more than once a week. In the study, the researchers asked 1, Danish men ages 18 to 28 whether they used marijuana and other drugs like amphetamine, ecstasy and cocaine within the past three months, and if so, how often. The researchers also collect semen samples, to measure the men's sperm counts and concentrations. About 45 percent of the men in the study said they had smoked marijuana in the past three months. About 10 percent of the study participants had used marijuana as well as recreational drugs during this time.