Cannabis has been used by sportspeople for millennia. The effects of tetrahydrocannabinol the principal psychoactive component in relation to aerobic exercise, strength or pharmacokinetics has been evaluated on a total of 15 occasions. Aerobic exercise performance is impaired, exercise induced bronchospasm is inhibited and strength is decreased. Plasma concentrations rise by <1ng/ml with exercise. Cannabis alters numerous psychological measures which accounts for the reported value for its use before during and after exercise. Cannabis has a spectrum of adverse effects on numerous psychological and physiological parameters which are ignored by those promoting its use in sport. The cardiovascular effects pose potential risks in individuals with any underlying cardiac pathology.