Marijuana is now legal for medical purposes in 29 states, and nine states allow it to be sold for recreational use. With broad claims made for its physiological and psychological value, cannabis is being used to treat seizures and glaucoma, reduce pain and inflammation, stimulate appetite, lessen stress, boost the immune system, and much more. It has also been widely adopted as a pathway to pleasure, raising questions about neurological effects, especially in the developing brains of teenagers. For decades, funding restrictions prevented US researchers from studying the science behind marijuana, but we’re finally learning more about how it works and where the risks and benefits lie.