Parahexyl (Synhexyl, n-hexyl-Δ3THC) is a synthetic homologue of THC, which was invented in 1949 during attempts to elucidate the structure of Δ9-THC, one of the active components of cannabis. 
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.  Parahexyl produces classic cannabis agonist effects in animals. It has a somewhat higher oral bioavailability than THC itself but is otherwise very similar.  Presumably it acts as a CB1agonist in the same way as THC but as there has been no research published using Parahexyl since the discovery of the CB1 receptor this has not been definitively confirmed.
Parahexyl was made illegal under UN convention in 1982 on the basis of its structural similarity and similar effects profile to THC, despite never having had any recorded instances of abuse by humans or illicit sale. Parahexyl was placed into the most restrictive Schedule 1 as a compound with no medical use.
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