Clinical effects and plasma levels of Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) in heavy and light users of cannabis

Abstract

Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) was administered in a crossover design by smoking and IV injection to groups of heavy and light users of marihuana. Plasma concentrations of Δ⁹-THC were similar for the groups after IV injection of 5.0 mg Δ⁹-THC, but the AUC_{0–240 min} showed a trend towards lower values for the heavy user group. To achieve a maximum desired “high”, both groups smoked similar amounts (about 13 mg) of Δ⁹-THC. Heavy users tended to have higher plasma levels than light users. The systemic availability of smoked Δ⁹-THC was significantly higher for the heavy users (heavy users 23±16% vs 10±7% for light users). These results also indicate that heavy cannabis users smoke more efficiently than casual smokers.

Both light and heavy users showed more clinical effect following IV administration than after smoking. The response of the heavy users, both with respect to effect on heart and “high”, was quite comparable to that of light users.

The present study does not suggest that tolerance readily develops in heavy users.