A joint study has found that cannabis users who exercise often give out positive drug test results.

The researchers asked a group of regular cannabis users, who had abstained from smoking overnight, to go through a fairly intense 35-minute workout on a stationary exercise bike. After completing the workout, the participants were tested and the researchers found a substantial increase in blood THC levels which was accompanied by a rise in free fatty acids in the blood.
“These results have potentially huge medico-legal implications. 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”, lead researcher Professor Iain McGregor said.
Source-Medindia