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Hair testing is a method of drug testing approved by the U.S. Food and Drug Administration. It's an optimal method for detecting long-term drug use because it can detect drugs used within the past 90 days. Hair testing is more expensive than other types of drug tests, such as urinalysis or saliva tests, but it's more accurate because the test cannot be fooled with detoxification products. Only the inside shaft of the hair is analyzed. Hair tests generally provide results within 24 to 72 hours of testing.
A hair test requires various strands of hair from the scalp, each at least 1/2 to 1 inch long. If scalp hairs cannot be obtained, body hair may be used. At least 40mg of hair must be obtained in total for valid test results. Various chemicals are applied to the hair sample to test for drug metabolites. If drugs have been used, the chemicals show the corresponding drug metabolites and indicate how long they have been in the body.
Hair testing can detect all major classes of drugs, such as marijuana, cocaine, opiates, methamphetamine and PCP. If requested, hair testing can also detect the presence of heavy metals, poisons and toxins, and alcohol. Hair tests use a process of confirmation that includes gas chromatography/mass spectrometry (GC/MS) in order to remove doubt about false test results. According to DrugTestingNetwork.com, hair tests provide "nearly twice the number of positives as urine testing," but they are not infallible because "after a drug is used, it takes about 7-10 days for the hair containing the drug to grow out of the scalp enough to be cut. Therefore, the hair test will not include drugs used in the week prior to the test."