Activity of $\Delta ^{8}$- and $\Delta ^{9}$-Tetrahydrocannabinol and Related Compounds in the Mouse

The 11-hydroxy metabolites of $\Delta ^{8}$- and $\Delta ^{9}$-tetrahydrocannabinol are more active than the parent compounds when administered to mice by either the intravenous or intracerebral route. Both $\Delta ^{8}$- and $\Delta ^{9}$-tetrahydrocannabinol are rapidly and extensively metabolized by the liver and not by the brain. The hypothesis that the 11-hydroxy metabolites may be the active form of tetrahydrocannabinol is discussed.