Precursor to metabolite: Venlafaxine XR to Desvenlafaxine

Venlafaxine XR is converted to Desvenlafaxine by CYP2D6.

The pair

Venlafaxine XR — Extended-release SNRI for depression and anxiety; withdrawal and hypertension limit it.
Desvenlafaxine — Active metabolite of venlafaxine; more balanced SNRI with simpler kinetics.

Anything that inhibits or induces CYP2D6 shifts the balance between Venlafaxine XR and Desvenlafaxine.