High school students whose friends posted photos of drinking and smoking were about 20 percent more likely to become drinkers or smokers themselves. iStockphoto hide caption

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The teenage years are the last golden opportunity to build a healthy brain, researchers say. So smoking pot might not be so smart. Tomas Rodriguez/Corbis hide caption

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Teenagers' sleep patterns may be a clue to their risk of depression. iStockphoto hide caption

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Even if you're under 25, you should still know your blood pressure, a study says. Rudyanto Wijaya/iStockphoto hide caption

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Smoking can mess up your looks, according to an ad campaign aimed at keeping teens from smoking. Courtesy of U.S. Food and Drug Administration hide caption

toggle caption Courtesy of U.S. Food and Drug Administration

Almost half of high-schoolers have had sexual intercourse, but teens almost never ask their doctors about sexual health. Nicole Young/iStockphoto hide caption

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