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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The 2014 Adventure Issue
From Iceland's Highway 1 to Utah's Canyonlands, an epic itinerary for modern explorers.
Plus: Building a Bigger Action Hero
ON NEWSSTANDS NOW
The Interpreters We Left Behind
The Rise of Cyclocross
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