Excessive alcohol intake can change the liver's metabolism. This, in turn, may raise estrogen and lower testosterone, a hormone change that is bad for fertility, says Dr. Thomas J. Walsh. Tobacco use has also been shown to lower semen quality and create abnormally shaped sperm. Pot isn't a safe choice either. Tetrahydrocannabinol (THC), the active ingredient in pot, is such a powerful inhibitor of sperm production that some researchers are looking into THC as a form of male birth control.
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