Decahydroisoquinoline is a nitrogen-containing heterocycle with the chemical formula C9H17N.

[1] It is the saturated form of isoquinoline.

Decahydroisoquinoline can be formed by the hydrogenation of isoquinoline or tetrahydroisoquinoline.

[2] There are four stereoisomers of decahydroisoquinoline which differ by the configuration of the two carbon atoms at the ring fusion: The decahydroisoquinoline occurs naturally in some alkaloids, including gephyrotoxins and pumiliotoxin C which are found in amphibian skins.

[3] A variety of pharmaceutical drugs include a decahydroisoquinoline ring system within their structure, including ciprefadol,[4] dasolampanel,[5] nelfinavir,[6] saquinavir,[7] and tezampanel.