The results of a news study has revealed that extreme stress and dieting can lead to a positive cannabis test, even long after the drug was last used.
Lead researcher Jonathon Arnold, from the University of Sydney in Australia, says that the main psychoactive ingredient of cannabis tetrahydrocannabinol (THC) is instantly absorbed by fat cells and over the next few days is slowly diffused back into the blood.
Since THC is taken up by fat more readily than it diffuses out, the researcher says that 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.
During the study, Arnold and colleague Iain McGregor exposed THC-laden fat cells taken from rats to the stress hormone ACTH.
The researchers found that the hormone increased the speed of release of THC from the cells.
They later injected rats with 10 milligrams per kilogram of THC (equivalent to a person smoking between five and 10 cannabis cigarettes, depending on their strength) every day for 10 days.
Two days later, they injected a third of the rats with ACTH, deprived another third of food for 24 hours, with the rest as controls.
They found that rats that were not given food had double the blood level of THC acid, a metabolite of THC, compared with the controls.
The other group exposed to ACTH also showed a statistically significant increase in THC acid levels.
Arnold said that 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,
"But the clincher would be for us to show these results in humans," New Scientist magazine quoted him as saying.
The study has been published in the British Journal of Pharmacology.