Tetrahydroharman, also known as 1-methyl-1,2,3,4-tetrahydro-β-carboline, is a general name for one of two isomers:

1. (1S)-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole
2. Calligonine ((1R)-1-methyl-2,3,4,9-tetrahydro-1H-pyrido[3,4-b]indole)

Calligonine is a major alkaloid constituent of the roots of Calligonum minimum and the bark of Elaeagnus angustifolia

Elaeagnus angustifolia

Elaeagnus angustifolia, commonly called silver berry, oleaster, Russian olive, or wild olive, is a species of Elaeagnus, native to western and central Asia, from southern Russia and Kazakhstan to Turkey and Iran...

. When taken internally, it has the effect of substantially lowering blood pressure for an extended period of time, similar to reserpine

Reserpine

Reserpine is an indole alkaloid antipsychotic and antihypertensive drug that has been used for the control of high blood pressure and for the relief of psychotic symptoms, although because of the development of better drugs for these purposes and because of its numerous side-effects, it is rarely...

.