Effects on Humans of $\Delta ^{9}$-Tetrahydrocannabinol Administered by Smoking

Twelve chronic marijuana users received $\Delta ^{9}$-tetrahydrocannabinol by smoking. The magnitude of their pulse increment was highly correlated with their subjective experiences. Three of the 12 subjects subsequently received $\Delta ^{9}$-tetrahydrocannabinol labeled with carbon-14; the time course of its concentration in plasma was highly correlated with the pulse increment. Subjective symptoms, however, appeared later and dissipated more slowly.