Requirements

• 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 instead. At least 40 mg of hair must be obtained in total for valid test results. The hair sample must be submitted to a laboratory and analyzed for drug use.
  
  

Procedure

• 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. The laboratory results are analyzed and interpreted as either "positive" or "negative" for the use of drugs.
  
  

Drug Detection

• Hair testing can detect all five major classes of drugs: marijuana, cocaine, opiates, amphetamine and phencyclidine (PCP). If requested, additional panels can be added to detect the presence of heavy metals, poisons and toxins and alcohol with a hair test. Hair testing is an optimal method for detecting long-term drug use because it can detect drugs used within a period of up to 90 days from testing.
  
  

Reliability

• The FDA-approved hair drug test cannot be fooled with detoxification products, such as shampoos, because only the inside shaft of the hair is analyzed. According to DrugTestingNetwork.com, hair tests uncover twice as many drug users as urinalysis tests, but they are not flawless; hair tests are incapable of detecting drugs used in the week prior to the test because it takes about a week for the hair containing the drug metabolites to grow out of the scalp enough to be cut.
  
  

Confirmation

• Hair tests use a process of confirmation that includes gas chromatography/mass spectrometry (GC/MS) in order to remove doubt about false test results. This is the same confirmation procedure used in forensic investigations and is therefore extremely precise.