Hair Testing
Testing hair for drugs of abuse, primarily Amphetamines, Cocaine, Opiates, and Phencyclidine (PCP) involves detecting drug use over an approximately 90-day period, 180-day period, or a 270-day period.
The regular, chronic user is most likely to show a positive result. When a drug is ingested it enters the blood stream and then chemical particles as components of these drugs are deposited in the cortex of the hair as a permanent part of the hair strand. Therefore, dyes, bleaches, and styling products will not affect the outcome of a hair test.
The reason that Marijuana is not included as part of the profile is due to inconclusive results. A small sample of hair from the scalp will be taken and then analyzed by the laboratory. It will first be washed and have its melanin (coloring) removed.