THC appears from smoking marijuana. It can remain in your body for up to 90 days but there are ways to fasten the natural process. First thing is to drink lots of water. Cranberry juice is also said to be good as it helps in the detoxification process. It is believed that exercising before the test helps remove THC from the body but you should not exercise immediately before taking the test. There are a many detoxication kits available online but their effectiveness is doubtful.