Dieting could lead to a positive test for cannabis

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.