Delta-11-Tetrahydrocannabinol (Delta-11-THC, Δ11-THC, Δ9(11)-THC, exo-Tetrahydrocannabinol) is a synthetic isomer of tetrahydrocannabinol, developed in the 1970s. It can be synthesised from Δ8-THC by several different routes,[1][2][3] though only the (6aR, 10aR) enantiomer is known. In animal studies it was found to be active in mice with around 1/4 the potency of Δ9-THC,[4] but did not substitute for THC in rhesus monkeys, probably because the dose tested was not high enough to produce cannabinoid-like effects.[5][6] It has been identified as a component of “vaping liquids” sold for use in humans.