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

While nearly half of the US has legalized the drug in some form, its national status has made comprehensive research into the drug's potential benefits (as well as its risks) has been all but impossible.

On November 8, three more states voted to make marijuana completely legal. California, Nevada, and Massachusetts all voted to support the legal use and sale of recreational marijuana. Here's what we know about how marijuana affects the brain and body:

Marijuana can make us feel good.