How Far Back Can a Hair Follicle Test for Drugs?

Hair follicle drug tests use a method of testing for controlled substances by using a sample of strands of hair from the head or body. These tests are often more effective than a urine test for detecting drug use over a longer period of time because hair strands serve as a record of drug consumption.

Significance

Hair follicle drug tests are an easy way to test for drugs, and these tests can detect drug use over a far longer span of time than other methods of testing for drugs. From the time of drug use, it takes about five days for a trace of drugs to get into a strand of hair.

Testing Hair

Every 1.5 centimeter of hair has a record that spans a month. The standard hair follicle drug test takes about 4 centimeters of hair, which tests for drug use in the past three months.

Detecting Drugs

Hair follice tests test for the following controlled substances: opium, crystal meth, marijuana, cocaine, ecstacy and PCP. These drugs all stay captured within a strand of hair indefinitely, until that part of the hair is cut off.

Using Other Hairs

Body hair can also be used for a hair follicle drug test. However, because body hair grows more slowly, doing a hair follice test with strands of body hair can catch drug use within the last year.

Taking the Test

The only foolproof way to test negative for drugs in a hair follicle test is to have been clean for the three months preceding the test. There are shampoos that claim to wash the drug traces out of hair, but these do not get at the traces of drugs inside the core of the hair.