Marijuana's official designation as a Schedule 1 drug — something with "no currently accepted medical use" — means it's pretty tough to study.

Yet both a growing body of research and numerous anecdotal reports link cannabis with several health benefits, including pain relief and helping with certain forms of epilepsy. In addition, researchers say there are many other ways marijuana might affect health that they want to better understand.

A massive report released in January helps sum up exactly what we know — and, perhaps more importantly, what we don't know — about the science of weed.

Marijuana can make you feel good.

One of weed's active ingredients, tetrahydrocannabinol, or THC, interacts with our brain's reward system, the part that's primed to respond to things that make us feel good, like eating and sex.

When overexcited by drugs, the reward system creates feelings of euphoria. This is also why some studies have suggested that excessive marijuana use can be a problem in some people — the more often you trigger that euphoria, the less you may feel during other rewarding experiences.

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