How can you clean thc out of your system before a drug test?

Stop Taking it: How long marijuana is detected in the urine depends strongly on frequency of use. In regular users (more than once a week), the marijuana metabolite THC-COOH builds up to a high level, often on the order of hundreds of nanograms per milliliter (ng/ml), from which it may take weeks to decline back below the threshold of detection. The situation is different for occasional users (no more than once a week), who often clear up in a couple of days.