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Passive Inhalers of Marijuana Smoke Can Test Positive, Study Says

November 24, 1986

BALTIMORE (AP) _ A person who sat in a room filled with marijuana smoke but did not himself use the drug could show a positive result in a urine test for drug usage, according to a federal study commissioned by the Navy.

But Navy officials said the findings confirm their position that anyone who tests above a certain threshold would have used the drug.

″Passive inhalation is a myth at the cutoff level we use,″ said Lt. Commander John Fenton.

The scientists who conducted the study, however, said the findings should caution the public and those who test for drug use.

″With sufficient time and high marijuana smoke exposure conditions, it becomes difficult to distinguish between active smoking and passive inhalation,″ Dr. Edward J. Cone and Dr. Rolley E. Johnson wrote in their report on the study.

A spokeswoman for the American Federation of Government Employees, which has opposed proposals for routine drug testing of its members, agreed.

″This is another situation that proves drug testing is not conclusive,″ said Jeannette Abrams.

The study was conducted last year by the National Institute on Drug Abuse’s Addiction Research Center in Baltimore. The findings were reported in a recent issue of Clinical Pharmacology and Therapeutics, a scientific journal.

Five volunteers were exposed to the smoke of 16 marijuana cigarettes in an unventilated room, 6 feet by 8 feet, an hour a day for six days.

The participants all had positive urine tests, on average lasting two to three days after the exposure ended, said Cone, chief of the chemistry and drug metabolism laboratory at the research center. One participant tested positive five days later, he said.

The marijuana was detected in a test whose sensitivity was 20 nanograms of tetrahydrocannabinol, or THC, the active ingredient of marijuana, per milliliter of urine. It also was detected when the cutoff level of the test was raised to 100 nanograms - the level used by the Navy. A nanogram is a billionth of a gram.

On other days, the same people were exposed to the smoke of four marijuana cigarettes, a situation more likely to mimic what could occur socially in normal settings outside of laboratories, Cone said. When exposed to the four cigarettes, the participants still tested positive for marijuana at the 20- nanogram level, but not when the testing level was raised to 75 nanograms.

″If 16 cigarettes in a closed-in room the size of my walk-in closet is passive smoking, then we have a problem,″ Fenton said. ″But I don’t think you’ll find that in the real world.″

The scientists who conducted the study said the findings should caution the public and those who test for drug use.

″With sufficient time and high marijuana smoke exposure conditions, it becomes difficult to distinguish between active smoking and passive inhalation,″ Cone and a colleague, Dr. Rolley E. Johnson, wrote in their report on the study.

As a result of the study, some laboratories that had been testing at the more sensitive level of 20 nanograms have raised their level to 100 nanograms to try to eliminate any passive smokers, Cone said.

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