Reserpine, an indole alkaloid, was extracted from Rauwolfia serpentina or Indian snakeroot. It has been in used in Indian medicine for several hundred years, and was a treatment for conditions that we might now recognise as mental illness. Gandhi is alleged to have taken it as a relaxant.
It showed antipsychotic effects and was used in the treatment of high blood pressure. It has subsequently been banned from use in the United Kingdom, because of severe, problematic side effects. These included severe depression and unexpected suicide.
One of its predominant effects on the brain was to deplete stores of monoamine neurotransmitters, such as adrenaline, noradrenaline, and dopamine.
This is one of the bits of evidence that lead to the formulation of what was to become known as the “monoamine theory” of depression, a theory that still holds a lot of influence up to the present day.
The current focus has been on Serotonin, another monoamine neurotransmitter in the brain.