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If you drink, smoke, or do drugs and you have fitness-obsessed friends who occasionally give you a hard time for your vices, you may want to print out this story from National Geographic, just so you have it handy the next time you run into them while you're on your way to a bar and they're headed to the gym. According to new research in the August issue of Behavioral Neuroscience, "Hardcore runners who can't bear to skip a workout may be hooked in a way that's similar to heroin addiction." And it can be fatal, too! [National Geographic]