Exercise increases plasma THC concentrations in regular cannabis users

Abstract

Background

The major psychoactive ingredient of cannabis, Δ⁹-tetrahydrocannabinol (THC) accumulates in fat tissue from where it slowly diffuses back into blood. THC pre-treated rats can show elevated plasma cannabinoid levels when subjected to conditions that promote fat utilization, such as fasting. Here we examine whether fasting and exercise increase plasma THC concentrations in regular cannabis users.

Methods

Fourteen regular cannabis users completed 35 min of exercise on a stationary bicycle in either a fed or overnight fasted state. Plasma cannabinoid levels were assessed prior to exercise, immediately post-exercise and 2 h post-exercise. Plasma samples were also analyzed for indices of lipolysis (free fatty acids (FFA) and glycerol).

Results

Exercise induced a small, statistically significant increase in plasma THC levels accompanied by increased plasma FFA and glycerol levels. Exercise-induced increases in plasma THC concentrations were positively correlated with body mass index. Fasting induced a significant increase in plasma FFA levels, and a lowering of blood glucose, but did not significantly alter plasma cannabinoid levels.

Conclusions

Here we demonstrate that exercise enhances plasma THC levels in regular cannabis users. The lack of a fasting effect may reflect the modest duration of fasting used which was associated with only a modest increase in fat utilization relative to exercise. Overall, these results suggest that exercise may elevate blood THC levels by releasing dormant THC from fat stores. These data suggest the interpretation of blood THC levels in roadside and workplace tests might be complicated by recent exercise.

Introduction

Cannabis is the most widely used illicit drug in the world and its use can promote cognitive and psychomotor impairment (Degenhardt and Hall, 2012, Ramaekers et al., 2011). Testing for cannabinoids is increasingly being performed at the roadside and in the workplace, with many countries implementing “zero tolerance” or per se limits on blood cannabinoid concentrations for driving, analogous to those imposed with alcohol (Bergamaschi et al., 2013, Vindenes et al., 2012). A cannabinoid positive test can have major repercussions for individuals through sanctions imposed by the criminal justice system or employers. This is despite considerable uncertainty as to whether a positive test necessarily indicates psychomotor impairment or recent cannabis use (Karschner et al., 2009b, Ramaekers et al., 2011).

The main psychoactive constituent of cannabis, Δ⁹-tetrahydrocannabinol (THC), is highly lipophilic, and accumulates in adipose tissue where it may remain for long durations (Kreuz and Axelrod, 1973). THC has been detected in human fat biopsies 28 days following exposure to cannabis (Johansson et al., 1989) and inpatient detoxification studies typically detect cannabinoids in heavy users after many days of abstinence (Karschner et al., 2009a, Karschner et al., 2009b). We have recently shown that fasting can increase blood cannabinoid concentrations in rats pre-treated with THC due to mobilization of THC from fat tissue undergoing metabolism (Gunasekaran et al., 2009). This suggests that blood cannabinoid concentrations in human cannabis users might be elevated under conditions of increased fat utilization, such as exercise, stress or fasting.

We examined here whether regular cannabis users subjected to fasting or exercise can display elevated plasma cannabinoids. We chose moderate intensity cycling as our exercise as it promotes lipolysis, particularly in fasted individuals (Achten and Jeukendrup, 2004). Cannabis users were subjected to moderate intensity exercise on a stationary bicycle either: (1) after a 12 h overnight fast, or (2) in a non-fasted condition. Plasma concentrations of THC and its metabolite THC-COOH were analyzed, as well as free fatty acids (FFA) and glycerol, two markers of lipolysis.