Cannabis has been hailed as a potential magic bullet in the fight against all sorts of ills, including chronic pain and depression. But it has also been called the “devil’s lettuce,” with claims that using it will lead to laziness, insanity and even murder. These polarized views can, in part, be explained by the drug’s complexity: cannabis is not a single substance but rather a mixture of more than 500 individual chemicals whose proportions vary from one plant strain to another.