Precursor to metabolite: Clozapine to Norclozapine

Clozapine is converted to Norclozapine by CYP1A2.

The pair

Clozapine — Most effective antipsychotic; used in treatment-resistant cases despite agranulocytosis risk.
Norclozapine — Active clozapine metabolite; M1 agonist implicated in some clozapine effects.

Anything that inhibits or induces CYP1A2 shifts the balance between Clozapine and Norclozapine.