But if you're feeling lucky and want to take your chances on dilution instead... remember that THC metabolites can be detected for up to 4 to 6 weeks after marijuana use. If you have more than a couple weeks notice, increasing your metabolism is probably the most effective way to decrease the time period that drugs can be detected in your system. The best ways to do that are to get lots of exercise, and eat lots of high-calorie foods... in that order. While exercising will clean THC metabolites from the system at a faster rate, lowering the detection period, it is important to stop burning those fat cells near test time, because the exercise actually increases the amount of THC metabolites in the urine, so you must quit exercising about a week before the test... then be lazy, and eat big and pack on some fresh, clean fat cells on top of the remaining older ones.
You should begin raising your creatinine levels, starting 2 or 3 days before the test. Creatine, which metabolizes into creatinine in 24 to 48 hours, can be raised with red meat and/or Creatine supplement, available online or at nutritional food stores such as GNC. However, any creatine taken within 24 hours of the test is useless as it will not have sufficient time to metabolize properly.
About 2 to 3 hours before the test, start drinking an 8 ounce glass of water quickly every 15 minutes, so that's about 1 quart or liter each hour. Instead of water you can substitute Gatorade, cranberry, grape or any fruit juice, coffee, iced tea, herbal tea, or soft drinks as they are all good diuretics. Diuretics make people urinate frequently. Diuretics without caffeine or alcohol are recommended because caffeine and alcohol have negative side effects. The best choice is Gatorade because of its electrolytes and high sodium content. After about an hour or so, you should be voiding clear urine about every 15 to 20 minutes. Be sure you have voided dilute urine at least 4 or 5 times before your test. Continue drinking 8 more ounces of water or Gatorade every 15 minutes to replace what you've urinated for a total of about 2-3 quarts in 2-3 hours. If you drink too much water, such as a gallon or more, your sample will be more likely to be rejected as being too diluted. Also drinking excessive amounts of water in the days, or even the night before the test doesn't really help.
At about 3 hours before the test, unless you are aspirin-sensitive, take 4 regular aspirin (not Advil or Tylenol) and also take 4 Rolaids or Tums antacid tablets. Then take 4 more aspirin and 4 more Rolaids again at about 2 hours before the test. Instead of causing a false positive, like ibuprofen/advil is known to do, aspirin actually acts a smoke screen interfering with the EMIT assay, and reduces positive readings for 2 to 12 hours.
At about 1 hour before the test, take a vitamin B2 or B-Complex, with 50 or 100mg of B2. However, if the vitamin is time released, you can either take it earlier with the first 2 glasses of water at about 3 hours before the test, or else you'll need to crush it before taking. Within 30 to 45 minutes of taking your B vitamin, your urine should turn from clear to yellow for the next few voids.