Acute effects of marihuana smoking on maximal exercise performance.

To evaluate the effects of marihuana smoking on exercise performance, 12 healthy young subjects did progressive exercise testing on an ergocycle to exhaustion under two conditions: non-smoking (control) and 10 min after smoking a marihuana cigarette (containing 1.7% of delta-9-tetra-hydro-cannabinol) of 7 mg X kg-1 body weight. Heart rate, arterial blood pressure, minute ventilation (VE), breathing rate (fb), oxygen uptake (VO2), and carbon dioxide output (VCO2) were measured before, during, and for 4 min after the exercise. Tidal volume was calculated from VE X fb-1. The exercise duration was also measured. Forced expiratory volume (FEV1) was measured: before smoking (rest); before exercise (10 min after smoking); and after exercise. Carboxyhemoglobin levels were measured before and 10 min after smoking in four subjects. Marihuana smoking reduced exercise duration (16.1 +/- 4.0 to 15.1 +/- 3.3 min, P less than 0.05). At peak exercise performance, there were no differences in VO2, VCO2, heart rate, and VE between the two experimental conditions. Marihuana induced tachycardia at preexercise (94.3 +/- 13.3 beats X min-1 to 119.0 +/- 18.0, P less than 0.01) that was sustained up to 80% of maximum effort and during the recovery period. After marihuana, VE, VO2 and VCO2 were increased above control from 50% of maximum effort to the end of the test. Marihuana induced a bronchodilation (FEV1 from 4.28 +/- 1.00 to 4.43 +/- 1.031, P less than 0.0) that was still present after exercise. Exercise induced a bronchodilation in the control condition but not in the marihuana smoking condition.(ABSTRACT TRUNCATED AT 250 WORDS)