If you’re a first-time smoker, it may take up to three days to fully clear your system of marijuana, depending on a variety of variables. The detection window for regular users is about 5 to 7 days. Those who smoke more than one joint each day will be tested positive for at least 30 days. But here’s the thing: we know that THC, the main ingredient in marijuana that drug tests check for, is stored in body fat. THC tends to remain in athletes’ systems for a shorter length of time because they have lower body fat and higher metabolic rates, which means fat is burnt faster and THC is released and eliminated faster.