Does sertraline make the pupil larger because of increased serotonin?

Not @ normal doses. At normal doses, sertraline does not usually cause mydriasis (pupillary dilatation). If someone overdoses or combines sertraline with other medicines that increase serotonin in the system, serotonin syndrome could result. Autonomic nervous system effects of serotonin syndrome include sweating, mydriasis, hypertension, tachycardia, hyperthermia, piloerection, and muscular rigidity.