Methods for making trans-(−)-Δ9-tetrahydrocannabinoI and trans-(+)-Δ9-tetrahydrocannabinol are disclosed herein. In one embodiment, a trans-(−)-Δ9-tetrahydrocannabinoI composition is prepared by allowing a composition comprising (±)-Δ9-tetrahydrocannabinol to separate on a chiral stationary phase to provide a trans-(−)-Δ9-tetrahydrocannabinoI composition comprising at least about 99% by weight of trans-(−)-Δ9-tetrahydrocannabinol based on the total amount of trans-(−)-Δ9-tetrahydrocannabinol and trans-(+)-Δ9-tetrahydrocannabinol. The invention also relates to methods for treating or preventing a condition such as pain comprising administering to a patient in need thereof an effective amount of a trans-(−)-Δ9-tetrahydrocannabinoI having a purity of at least about 98% based on the total weight of cannabinoids.