cis-Delta-9-Tetrahydrocannabinol ((-)-cis-ÃÂ<sup>9</sup>-THC) is an isomer of tetrahydrocannabinol found in the Cannabis plant but in lower quantities than the more well-known trans isomer. Formation of cis-THC could take place in process of epimerization associated with acid-catalyzed cyclization of CBD to THC. It has similar psychoactive effects to trans-ÃÂ<sup>9</sup>-THC in tests on mice, but with only around 1/5th the potency. The equivalent ÃÂ<sup>8</sup> isomer is also known as a synthetic compound, but has not been isolated from Cannabis plant material. All four cis/trans isomers are known, though only the (6aR,10aR) and (6aS,10aR) enantiomers are psychoactive, while the others retain activity at targets such as GPR18 and GPR55.