Most of us discovered the mood-boosting powers of chocolate by age 2. And it's no surprise that we get hooked on it young: Studies have shown that chocolate contains chemical compounds that can have similar effects on the brain as marijuana. Some think chocolate's power comes from serotonin-boosting carbs; others say it has chemicals that boost dopamine; still others say it's the pleasure from satisfying your craving that cheers you up. Regardless of the reason, many people report feeling better after a few squares (of course, they feel worse—or at least guiltier—after eating a lot of squares).
Added perk: The caffeine in the chocolate can also rev up your energy.