Can methadone be detected on a hair test?

The test can go back as long as your hair is long. The average growth rate for hair is 1/2 inch every month. So if they take 2 inches of hair - they can test for four months worth of drug usage.

With said, however, the average hair drug test will go back for 30 - 90 days. The longer the hair is, the less accurate the test will be.