When you ask the question “How long does marijuana stay in your system?” you need to take into account the fact that there is no simple answer to this question. Quite simply, it’s argued both that THC never leaves your brain, as well as that there are several different factors which can affect whether or not you test positive for marijuana use.
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.