We study the behavioral changes due to marijuana consumption on fertility and its key mechanisms, as opposed to physiological changes. We can employ several large proprietary data sets, including the 1997 National Longitudinal Survey of Youth, Nielsen Retail Scanner database, as well as the Vital Statistics Natality files and apply a differences-in-differences approach by exploiting the timing of the introduction of medical marijuana laws among states. We first replicate the earlier literature by showing that marijuana use increases after the passage of medical marijuana laws. Our novel results reveal that birth rates increased after the passage of a law corresponding to increased frequency of sexual intercourse, decreased purchase of condoms and suggestive evidence on decreased condom use during sex. More sex and less contraceptive use may be attributed to behavioral responses such as increased attention to the immediate hedonic effects of sexual contact, delayed discounting and ignoring costs associated with risky sex. These findings are consistent with a large observational literature linking marijuana use with increased sexual activity and multiple partners. Our findings are robust to a broad set of tests.