Tests for Marijuana Flawed, Chemist Says

A chemist who testifies frequently in court cases on drug abuse said Tuesday that pigments in dark-skinned people break down into chemical fragments similar to the active ingredient in marijuana, leading to wrongful accusations of marijuana use based on inaccurate urine tests.

The chemist, James Woodford of Atlanta, who is self-employed as a consultant and expert witness on matters concerning drug testing, said the problem appears in highly sensitive urine tests for marijuana, where various contaminants in urine can alter the results of the tests.

Woodford’s theory has been disputed by Mahmoud ElSohly, a professor at the University of Mississippi. ElSohly said he had tested chemical products resulting from the breakdown of the pigment, melanin, and found that the products could not be confused with THC, or tetrahydrocannabinol, the active ingredient in marijuana.

Melanin is present in everyone, but in higher levels in blacks and Latinos, for example, than in whites, Woodford said in a telephone interview.