Parahexyl, also known as synhexyl, is a synthetic homologue of tetrahydrocannabinol (THC) which was invented in 1941 during attempts to elucidate the structure of Δ9-THC, one of the active components of cannabis.

[2][3][4] Parahexyl is similar in both structure and activity to THC, differing only in the position of one double bond and the lengthening of the 3-pentyl chain by one CH2 group to n-hexyl.

[5] Parahexyl produces effects typical of other cannabinoid receptor agonists in animals.

Parahexyl was occasionally used as an anxiolytic in the mid-20th century, the dosage ranging from 5 mg to 90 mg.[7][8] Parahexyl was made illegal under UN convention in 1971 on the basis of its structural similarity and similar effects profile to THC.

Parahexyl itself (i.e. the Δ6a(10a) isomer) has not had any significant use in scientific research since it was banned internationally in the early 1980s; however, the Δ8 and Δ9 isomers are both known to be cannabinoid receptor agonists, and Δ8-parahexyl has the code number JWH-124,[10][11] while Δ9-parahexyl has been isolated from Cannabis plant material and assigned the name tetrahydrocannabihexol (THCH).