Exercising before a drug test increases your chances of testing positive for marijuana.
The problem with testing for THC is that – unlike other drug metabolites – THC is stored in the fat cells of regular marijuana users. Previous studies show that it can stick around for about a month – in some cases, up to six months – since last use.
Now a team of Australian scientists have shown that exercise can lead to a spike in blood THC due to the burning of fat. Their results were published online in the journal Drug Alcohol and Dependence.
Lead author Iain McGregor, a professor of pharmacology at the University of Sydney, explained the implications of his findings to ABC Science.
“Someone subjected to workplace or roadside drug testing after a visit to the gym could end up testing positive despite an absence of recent cannabis use.”
What’s more, the study showed that people with higher BMIs experienced this effect to a greater degree. More obese individuals had the highest levels of THC in their blood, regardless of how much cannabis they used the previous day.
“The more fat you have in your body the bigger the reservoir you have for THC,” explained McGregor.
Researchers recruited 14 regular cannabis users and took blood samples from them before and after 35 minutes of exercise on a stationary bicycle.
While the spike in blood THC did not seem to cause a high, it was significant enough to be noticed on a standard drug test.
McGregor believes the findings have widespread implications.
“Someone caught in a bad car accident … the stress could cause them to burn fat and raise their THC, and they could give a positive drug test.”
The team plans to repeat the study on a larger group of patients in order to provide further insight into fat burning and THC levels.
The study was published ahead of print and received funding from the National Cannabis Prevention and Information Centre (NCPIC) and from the National Health and Medical Research Council of Australia.