Cannabis is considered a prohibited drug by the World Anti-Doping Agency (WADA). In 2011, the WADA published a paper  discussing the reasons why cannabis was considered a prohibited drug. The paper cited the following three criteria:
“Athletes who smoke cannabis or Spice in-competition potentially endanger themselves and others because of increased risk taking, slower reaction times and poor executive function or decision making.”
“Based on current animal and human studies as well as on interviews with athletes and information from the field, cannabis can be performance enhancing for some athletes and sports disciplines.”
“Use of illicit drugs that are harmful to health and that may have performance-enhancing properties is not consistent with the athlete as a role model for young people around the world”.
A recently completed study  that was published in the Journal of Cannabis challenges validity of the second point. The study involved a comprehensive review of literature that had been published on the topic up until January 2020. It specifically focused on the markers of physical performance, including maximum oxygen uptake (VO2max) and physical work capacity (PWC).
The research found that the only physiological measure that was impacted by cannabis consumption was resting heartrate, with regular users returning higher resting heartrates than non-users. There were no significant differences in any of the other predictors of athletic performance, suggesting chronic cannabis consumption has no significant performance enhancing properties. This study did not assess other aspects of athlete performance such as recovery or endurance, nor did it take into account the analgesic effect of the plant which could have benefits in some contact sports.
 Cannabis in Sport: Anti-Doping Perspective Marilyn A. Huestis1, Irene Mazzoni2, and Olivier Rabin2 1 Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD, USA
 Kramer, A., Sinclair, J., Sharpe, L. et al. Chronic cannabis consumption and physical exercise performance in healthy adults: a systematic review. J Cannabis Res 2, 34 (2020). https://doi.org/10.1186/s42238-020-00037-x