Abstract: An individual tetrahydrocannabinol isomer of interest is separated from a mixture containing two or more such isomers, by treating the mixture with an isocyanate or isothiocyanate of formula I: R—(CH2)n—N?C?X??(I) where R represents an aromatic ring optionally substituted with one or more electron withdrawing groups, n=0 or 1 and X is oxygen or sulphur; so as to produce a crystallizable THC carbamate of formula II: wherein X and R are as defined above, R? is a C3-C10 alkyl group and the dotted lines indicate optional unsaturation including aromatic, separating the compound of formula II from solution in isolation of other THC derivatives, and hydrolyzing the compound of formula II to form the individual tetrahydrocannabinol isomer of interest.