Short communication: Urinary excretion of 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol in a pregnant woman following heavy, chronic cannabis use.

Differentiating new intake of drugs-of-abuse from residual drug excretion may be difficult, especially following chronic drug usage and for drugs with long elimination half-lives such as cannabis. In the present case, cannabis was found in the urine of a young pregnant woman following heavy and chronic cannabis use. She was warned that if she continued using cannabis while pregnant she would be forced to be hospitalized. She was subjected to serial urine testing with 2-7-day intervals. Urinary 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (THCCOOH) concentrations, measured by liquid chromatography-mass spectrometry, declined from 348 to 3.9 ng/mL over a surprisingly long period of 12 weeks (84 days). Several algorithms for detecting new drug intake were applied during this time course; most indicated that the woman continued to smoke cannabis following the first urine test. The woman denied any use after the first specimen collection. In retrospect, her THCCOOH excretion profile supports her story. Algorithms for detecting new drug intake have been validated for occasional cannabis users only. We advise caution when interpreting urine test results from heavy, chronic cannabis users, especially when serious consequences are involved.