The chemical reactions in your body are the result of any usage and need to be corrected as soon as you know that you are going to have to give a drug test. If you need to know how to pass a drug test in 2 days, bear in mind that one of the most widely used methods of beating a drug test is to have any drug-free friend of yours supply the sample as your own. However, this is a little hard to pull off as it would require your friend being around at the time of collection. If a court has ordered the drug test, it is unlikely that you will be allowed to provide the sample without supervision.
Another method is to completely dilute the chemical presence in the body by drinking large amounts of water over the course of the timeframe you have before collection of the sample. The more water you drink - the more you urinate and dilute the toxins within the body. While the technician or doctor in the lab who actually performs the drug test on your urine will identify something being wrong with the sample as a result of the excess amount of water present, the sample itself will be inconclusive - preventing it from being positive.
There are also a number of detox kits available at various medical stores all over the country and can prove to be rather helpful.