Go ahead and pump it up potheads. You may be getting ripped but your brain is to fried to know what your doing.

Reformed cannabis users opting for a crash diet and gruelling exercise regime stand a greater chance of “retoxifying” than coming clean, a study has found.

An Australian finding, published in the British Journal of Pharmacology, found that stress or extreme dieting could trigger a release of THC, the psychoactive cannabis ingredient stored in fat, back into the bloodstream.

Co-author Jonathon Arnold, a senior lecturer in pharmacology from the University of Sydney, said the researchers studied rats after noticing unusual results in humans. “I had a case where a guy swears blind that he hadn’t consumed cannabis,” he said.

“But he’d gone on a vigorous weight-loss regime, lost four kilograms within a week and got this exceptionally high cannabinoid level that he couldn’t really explain.”

Dr Arnold’s colleague, Iain McGregor, injected rats with a THC-equivalent of smoking between five and 10 cannabis cigarettes a day for 10 days, before sending them cold turkey and exposing them to a stress hormone or depriving them of food.

In the hungry rats, the THC reading was more than double that of the control group. There was a statistically significant increase in stressed rats.

Dr Arnold said the implications for humans were being studied.

“You could potentially kick your grass habit and a couple of weeks later go on a rigorous diet and exercise regime . . . the THC could flood out,” he said.

Following a weekend binge by skipping breakfast and heading to the gym on Monday morning “could possibly lead them to say some silly things in a meeting”.

Jan Copeland of the National Cannabis Prevention and Information Centre said it was a case of user beware.

“Frequent cannabis users who make health lifestyle choices that include quitting cannabis in association with a diet and exercise regime need to be aware that they may still test positive for cannabis for . . . up to four weeks or even longer,” she said.

“Those for whom a negative test is critical should have a confidential test done by their GP.”