Precursor to metabolite: Quetiapine to Norquetiapine

Quetiapine is converted to Norquetiapine by CYP3A4.

The pair

Quetiapine — Sedating atypical for schizophrenia and bipolar depression; metabolic burden at any dose.
Norquetiapine — Quetiapine's active metabolite, and the source of the norepinephrine reuptake block and muscarinic blockade the parent lacks.

Anything that inhibits or induces CYP3A4 shifts the balance between Quetiapine and Norquetiapine.