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.
Not only that, but your metabolism and how much marijuana you smoked will also have an effect on the length of time that it will take before you can test without testing positive for marijuana use. After all, the half-life is only the length of time that it takes for you to lose half of the THC that is in your system. If you’ve smoked a lot of marijuana, then it will take you longer before the THC in your body drops back below the amount that is detectable by most drug tests.
For this reason, when you ask “How long does marijuana stay in your system?” you have to realize that it’s very unlikely that you’ll be able to get a usable answer. The most common period of time is anywhere from 3-30 days, depending on your metabolism and the amount of marijuana that you’ve smoked. This is unfortunate, since it means that while most drug tests can only turn up evidence of other drugs if you’ve been taking the drug within a few days of the drug test, marijuana could still be detected in a urine test up to a month after the last time it is used.
Hair tests are even worse, since your body stores THC in the hair follicles. For this reason, the previous answers to “How long does marijuana stay in your system?” are only useful if you’re going to be forced to take a urine test. For the hair test, depending on the amount of hair that the company takes, it’s possible that marijuana could be detected up to three years after the last time that you smoke. However, I have heard that the standard maximum detection period for a hair test is usually closer to 90 days.