Hair Drug Analysis

Hair testing for drugs has several advantages to urine drug testing. The sample is about 100 hairs twirled into a strand about the diameter of a pencil, and obtained from the back of the neck, or the back of the head. There is no cosmetic effect with this small sample removed. Of course, there is no collection embarrassment, and there is no way to dilute or alter the sample, as there is with urine. Hair grows about 1/2 inch each month, so with 1.5 inches of hair, one can evaluate past drug use for roughly 90 days. This makes this method valuable for pre-employment or random testing.

The disadvantages are that the testing is more expensive than urine drug testing, and since hair grows slowly, it is not useful for determining very recent use (post accident or reasonable suspicion testing), and hair analysisis not approved for D.O.T. drug testing. Also, for very light marijuana use ( e.g. one to three joints per month), hair testing may not demonstrate the presence at such a low dosage. However, in dual testing (both urine and hair) studies, hair testing has demonstrated up to 6 times greater efficiency in identifying marijuana use. The reason is that hair testing looks at 90 days of experience, whereas urine testing at best only evaluates a surveillance window of 1 to 3 days.

One should limit the sample size to 1.5 inches ( ~ 90 days). The reason is that especially with female hair, various chemical manipulations, such as geting a perm, dye and bleaching hair may remove virtually all soluable chemicals from the hair. Particularly if a woman gets her hair stripped and dyed, that process will extract drugs, vitamins, minerals from the hair. Apparantly the number of times that hair is treated will decrease the probability of drug detection.


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