New Scientist: Dieting could lead to a positive test for cannabis

[Heidi]

CANNABIS smokers beware: stress or dieting might trigger "reintoxication", resulting in a positive drug test long after you last used the drug.

The main psychoactive ingredient of cannabis is tetrahydrocannabinol (THC), and once in the body it is readily absorbed into fat cells. Over the next few days it slowly diffuses back into the blood. Since THC is taken up by fat more readily than it diffuses out, continual intake means some THC can remain in the fat cells.

It has been suggested that stored THC can be released at a later date in situations where the body's fat is rapidly broken down. This is based on anecdotal reports of spikes in blood cannabinoid levels in people who have not taken the drug recently but have experienced extreme stress or rapid weight loss.

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Subsequent blood tests showed that rats that were food deprived had double the blood level of THC acid, a metabolite of THC, compared with the controls. Those that were exposed to ACTH also showed a statistically significant increase in THC acid levels. The study has been accepted for publication by the British Journal of Pharmacology.

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The main implication of the work could be for legal cases in which athletes or employees have tested positive for cannabis but claim they haven't recently consumed it, Arnold says. "But the clincher would be for us to show these results in humans."

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