Anabolic Steroids
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Anabolic steroids, which are synthetic variations of testosterone, are legally prescribed to treat side effects of low testosterone and to help build muscle mass in men battling serious diseases like cancer and AIDS. But they are often used and abused by otherwise healthy guys who just want to bulk up. And yes, they're addictive. Steroids won't get you high, but they still mess with brain chemicals. Using them continually can cause severe mood swings, irritability, paranoia, and aggression. Even worse, they damage the kidneys, liver, and heart.

Even if you'd never dream of taking 'roids, you can still come across this junk in steroid-spiked products masquerading as dietary supplements. Beware of any muscle-building "supplements" being peddled online or in the locker room.