Acute Urinary Retention Following Low‐Dose Risperidone in a Young Woman: A Case Report

Risperidone is a widely used antipsychotic for psychotic disorders and is also used as an adjunctive treatment for many psychiatric conditions. While acute urinary retention is more commonly associated with antipsychotics that have anticholinergic effects, it is a rare adverse effect of risperidone. This report describes a 25‐year‐old woman with comorbid obsessive–compulsive and bipolar I disorders who developed acute urinary retention 3 days after risperidone was increased to 2 mg/day while on multiple psychotropic medications, including procyclidine, fluoxetine, aripiprazole, lamotrigine, and lithium. Clinical, laboratory, and radiological evaluations revealed no evidence of obstructive, neurological, or infectious causes. Risperidone was discontinued, and spontaneous voiding resumed within 48 h. The temporal association supports a key role of risperidone, although drug–drug interactions remain a potential contributing factor. The proposed mechanism involves risperidone’s antagonism of H1, D2, α1‐adrenergic, and serotonergic receptors, which may increase urethral sphincter tone and reduce detrusor contractility. Fluoxetine coadministration may exacerbate this effect by inhibiting cytochrome P450 (CYP) 2D6, thereby increasing plasma risperidone levels. Although rare, clinicians should remain vigilant for acute urinary retention while using risperidone, especially in the context of polypharmacy.