[2][3] As a secondary amine, tetrahydroisoquinoline has weakly basic properties and forms salts with strong acids.

[4] Tetrahydroisoquinoline derivatives may be formed in the body as metabolites of some drugs, and this was once thought to be involved in the development of alcoholism.

[5] This theory has now been discredited and is no longer generally accepted by the scientific community,[6] but endogenous production of neurotoxic tetrahydroisoquinoline derivatives such as norsalsolinol continue to be investigated as possible causes for some conditions such as Parkinson's disease.

[7][8][9][10][11][12] The tetrahydroisoquinoline skeleton is present in a number of drugs,[3] such as tubocurarine, one of the quaternary ammonium muscle relaxants.

Esproquin,[16] which shows hypotensive activity by virtue of its α-adrenergic blocking properties, is made from THIQ.