How long does it take for marijuana to leave your body?

The speed at which marijuana leaves your body depends both on the speed of your metabolism, as well as on the half life of THC. Unlike most other substances, the half-life of THC can vary quite a bit, depending on who is using it, when it's used, and several other factors. For example, it's estimated that THC can have a half life that ranges anywhere from 1-10 days. It's almost impossible to find out what that half life is, which means that it is very difficult to use it to calculate how long it will take for all of the THC to leave your body.