In recent years, cannabidiol – or CBD, as it is more commonly known – has become increasingly popular both in clinical research circles and among the general population. This growing popularity is due to the considerable therapeutic potential of the cannabinoid as demonstrated by clinical trials and historic evidence. Access to cannabis-based medicines is widening for a number of conditions, perhaps most notably in paediatric treatment-resistant epilepsy. Other proposed benefits include anxiolytic (anti-anxiety), antipsychotic, analgesic, anti-inflammatory, and neuroprotective effects.
This range of effects has been suggested as being promising for use by athletes. This theory is perpetuated by the increasing availability of low-dose CBD products that are marketed specifically to athletes in countries including the UK, Canada, and the US. Furthermore, CBD was recently removed from the World Anti-Doping Agency’s list of banned substances – a move that will further facilitate the use of CBD-based products among athletes.
The use of CBD in athletes is a lot more than just a theory; in fact, a recent survey found that 26% of British professional rugby players were either currently using or had previously used CBD. Reasons given for CBD use by these athletes included enhanced recovery (80%), improve sleep (78%), reduce anxiety (32%) and for “other’ medical purposes (14%). The clear increase in CBD use among athletes in recent years led researchers to investigate effects of acute, oral CBD treatment on physiological and psychological responses to exercise.
Design and Methods of the Study
The current randomised, placebo-controlled exploratory pilot trial involved a small sample of nine participants (endurance-trained males) given an oral formulation of either CBD (300mg) or placebo in two treatment sessions. The participants were asked to maintain their usual lifestyle, including diet and exercise patterns and to avoid using cannabis and other cannabinoid-based products throughout the study period.
To understand the effects of CBD in exercise, the individuals completed two running exercises per treatment arm. The first was a 60-minute fixed submaximal run followed by an incremental maximal run to exhaustion. Either CBD or placebo formulation was administered 1.5 hours before exercise in a randomised, double-blind design.
The researchers then measured respiratory gases ((V̇O2), respiratory exchange ratio (RER), heart rate (HR), blood glucose (BG) and lactate (BL) concentrations, and ratings of perceived exertion (RPE) and pleasure–displeasure were measured at three timepoints (T1–3) during RUN 1. V̇O2max, RERmax, HRmax and time to exhaustion (TTE) were recorded during RUN 2. Venous blood was drawn at Baseline, Pre- and Post-RUN 1, Post-RUN 2 and 1-hour Post-RUN 2.
What did the study show?
The data collected during this study indicated that oral CBD treatment may alter several key parameters, including submaximal (V̇O2) and maximal (V̇O2max) oxygen consumption, feelings of pleasure during submaximal exercise and markers of exercise-induced inflammation. Small effects were also detected in other parameters; however, the results were uncertain at many timepoints. The researchers note that the analytical approach used to collect this data was selected to inform the design of future “definitive” trials and recommend that the initial results should be interpreted with caution.
CBD appeared to improve ratings of pleasure during the first 40 minutes of submaximal exercise but there was no difference between 40 minutes and 60 minutes. The researchers note that participants may have felt better at 60 minutes because they knew they were close to finishing; therefore, the results at 60 minutes should be interpreted with caution. All participants also recorded very low absolute scores for anxiety and other mood alteration across both treatment arms.
Exercise was seen to increase the serum concentrations of various biomarkers of systemic inflammation, muscle damage, and gastrointestinal damage. Interestingly, CBD was seen to suppress the exercise-induced increase in pro-inflammatory cytokine IL-1β, Post-RUN 2 and 1-h Post-RUN 2. On the other hand, CBD appeared to increase Mb (a biomarker of muscle damage) suggesting an exacerbation of muscle damage. In contrast to some preliminary evidence to suggest that CBD may protect against some forms of GI damage, in the current trial, the cannabinoid did not seem to impact on lipopolysaccharide GI damage biomarkers.
Finally, the levels of anandamide concentration (an endogenous cannabinoid produced naturally in the body) varied at different points throughout the study. In all nine participants, plasma anandamide concentrations (1) decreased from Baseline to Pre-RUN 1; and (2) increased from Pre-RUN 1 to Post-RUN 1, regardless of the treatment administered. The researchers note that these effects were likely linked to breakfast consumption and the completion of submaximal exercise, respectively.
CBD appeared to decrease plasma anandamide concentrations Post-RUN 2 relative to placebo. This finding was contrary to the results of the only other study to have investigated the effect of CBD on circulating endocannabinoids which found that chronic CBD treatment increased (resting) serum anandamide concentrations in patients with schizophrenia. It should be noted, however, that the participant population, dosing regimen and experimental paradigm differed significantly between the two studies.
Throughout the discussion of this study, the researchers warn that the results recorded throughout the trial period should be interpreted with caution due to the design and intentions of the research. The pilot trial was not designed to formally assess “effect” of CBD but rather to gain a preliminary understanding of CBD’s effects on exercise physiology and determine whether these are worthy of further investigation.
In conclusion, however, these preliminary results suggest that acute, oral CBD treatment has the potential to alter key physiological and psychological responses during aerobic exercise. The authors note that the effects of CBD on V̇O2 responses, feelings of pleasure during exercise and exercise-induced inflammation appear to be worthy of further investigation. The results also suggest that CBD is unlikely to impair aerobic exercise performance in the study population which may support its use in a sporting context.