University of Sydney
Wednesday 11 September 2013, 01:52PM
Media release from the University of Sydney
Exercise is essential to a healthy lifestyle, but new research led
by the University of Sydney shows that for cannabis users, it could
also lead to positive drug tests.
Tetrahydrocannabinol (THC), the main intoxicating ingredient in
cannabis, has a strong affinity for fat tissue. Most of the THC
consumed when cannabis is smoked ends up being rapidly transferred
from the bloodstream into fat cells, where it accumulates and can
lie dormant for weeks or even months.
But what happens when you burn the fat that contains this
The study by researchers from the University of Sydney and
University of NSW, published in the most recent issue of Drug and
Alcohol Dependence, asked regular cannabis users to exercise at a
level that would cause fat to be metabolised - a reasonably tough
35-minute workout on a stationary exercise bike. The cannabis users
had all abstained from smoking overnight to ensure low blood levels
of THC prior to the exercise.
After the exercise, the researchers found a substantial increase in
blood THC in the cannabis users, which in some cases was enough to
make the difference between a negative and positive drug test. The
rise in blood THC was accompanied by a jump in free fatty acids in
the blood, a tell-tale sign that fat was being used as a fuel
during the workout.
In an interesting twist, researchers found that the higher the
person's body mass index (BMI), the greater their increase in blood
THC levels with exercise. According to the researchers, greater
body fat usually accompanies a higher BMI, resulting in a larger
reservoir of stored THC that can be released during exercise.
"These results have potentially huge medico-legal implications,"
says Professor Iain McGregor, from the University of Sydney's
School of Psychology, who led the research.
"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.
In addition, it may not just be exercise that produces this effect.
Other things that increase use of body fat, for example dieting, or
physical or psychological stress, might produce a similar or even
The study also looked at the effects of a 12-hour fast on blood THC
levels in some users, although this manipulation failed to increase
THC in the same way as exercise. The researchers noted that more
than 12 hours of fasting may be required to kick fat use into the
high gear required to liberate THC.
Future studies are planned to examine whether the raised THC caused
by exercise is enough to impair driving ability and memory in
Professor Iain McGregor is available for interview on 02 9351 3571
or 0418 765 185, or at email@example.com
The research paper can be found at:
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