Effects of smoked marijuana of varying potency on ventilatory drive and metabolic rate.

Ventilatory responses to hypercapnia in experienced marijuana smokers have previously been shown to decrease, increase, or not change acutely after marijuana. In one study, minute ventilation (VE) and O2 consumption (VO2) increased but hypoxic ventilatory response did not change after smoking marijuana. We further investigated the effects of marijuana of increasing potency (0, 13, and 20 mg THC) on ventilatory and mouth occlusion pressure (P0.1) responses to hypercapnia and hypoxia in 11 young, healthy men who smoked marijuana regularly but refrained from any smoked substance, alcohol, caffeine, or other drugs for greater than or equal to 12 h before study. Ventilatory and P0.1 responses to hypoxia and hypercapnia were measured on 3 separate days before and 5 and 35 min (hypoxia) and 15 and 45 min (hypercapnia) after smoking. In a companion 3-day study, 12 young male habitual marijuana smokers underwent measurements of VE, VO2, and CO2 production (VCO2) before and 5 to 135 min after smoking marijuana containing 0, 15, or 27 mg THC. None of the active marijuana preparations caused significant changes in ventilatory or P0.1 responses to either hypercapnia or hypoxia or in resting VE, VO2 or VCO2. We conclude that smoking marijuana (13 to 27 mg THC) has no acute effect on central or peripheral ventilatory drive or metabolic rate in habitual marijuana smokers. These conclusions cannot be applied to infrequent users of marijuana without further study.