Washington State University studied mice in order to see how cannabis affects the sperm in the male mice. In this study, researchers studies 30 adult male mice, exposing half of those mice to cannabis vapor three times a day for ten days, mimicking how frequent cannabis users intake daily. Researchers then compared these mice to the unexposed control group. They found that immediately right after the exposure period, the mice's sperm motility decreased and in one month, their sperm counts were found to have been lowered.
The researchers then went to breed several of the male mice to unexposed female mice to observe the outcome of the second generation of sons. The cannabis-exposed sons also showed evidence of DNA damage was related to sperm cell development. Kanako, one of the researchers said that the, "reduction in sperm count and motility of the off-sparing sons, is probably a direct effect of the cannabis exposure to the father."
In the third-generation, the grandsons of the exposed male mice did not show any DNA damage to that generation of sons. This suggests that the cannabis exposure only impacted the second-generation of mice.