Marijuana tests aren't foolproof, and some test-takers put a lot of effort into proving it.
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URINE TEST - 1. CHEATING BY ALTERING THE SAMPLE: Products with names such as Whizzies and Klear are additives that claim to alter or destroy evidence of drugs. Other products -- some as simple as table salt and baking soda -- can compromise tests.
URINE TEST - 2. CHEATING BY FLUSHING THE SYSTEM: Some herbal and other over-the-counter products -- mostly diuretics -- claim to rid the body of marijuana, but samples that are too clear may draw suspicion.
URINE TEST - 3. CHEATING BY SUBSTITUTION: This means replacing the sample with someone else’s urine using devices such as the Whizzinator or synthetic urine kits such as Fake It. The problems include leaky containers and temperature control.
BLOOD TEST: It's tough to cheat on a blood test. There are no counter measures available.
SALIVA TEST: Cheaters try to minimize the absorption of saliva by holding the swab against the teeth instead of gums. A monitor can notice this, however, and if the swab isn’t sufficiently moist a person can be retested.
HAIR TEST: Shaving head and body hair can make it impossible to supply an accurate sample. Heavy use of shampoo, vinegar and other substances on the hair also can interfere with detection.