An 18-year-old male with no significant past medical history was admitted to the psychiatric inpatient unit due to an acute psychotic episode. The clinical presentation included paranoid delusions, behavioral disorganization, and marked agitation, occurring in the setting of recent cannabis use. A diagnosis of cannabis-induced psychosis was established. There was no personal or family history suggestive of hematologic conditions, urologic disorders, or prior episodes of priapism. No additional substance use was reported beyond cannabis, and there was no exposure to medications commonly linked to priapism. Cannabis use was considered a potential contributing factor; however, current evidence does not support a consistent direct association with priapism, and no use of other substances, such as cocaine or vasoactive agents, was reported.

Given the broad differential diagnosis of priapism, potential etiologies were systematically considered. Hematologic causes, particularly sickle cell disease, were considered less likely based on the absence of suggestive history and unremarkable laboratory findings, although they cannot be completely excluded. Drug-induced causes were reviewed, with no exposure to medications commonly associated with priapism other than risperidone, which had been recently initiated prior to symptom onset. There was no history of perineal trauma, malignancy, or use of vasoactive substances. No clinical or laboratory findings supported an alternative etiology. The absence of prior episodes and the temporal relationship between long-acting risperidone administration and symptom onset further supported a drug-induced mechanism.

Oral risperidone was initiated and progressively titrated to 9 mg daily to achieve symptom control after partial response at lower doses, resulting in significant symptomatic improvement and remission of psychotic features. Although most patients respond within the 2-8 mg/day range, higher doses may be required in some cases. This higher dose is reported to document overall exposure preceding the event, as antipsychotic-associated priapism is not clearly dose-dependent but rather related to pharmacodynamic mechanisms, including α1-adrenergic receptor blockade. Given concerns regarding long-term adherence, a transition to a long-acting injectable risperidone formulation was planned, and a 100 mg monthly intramuscular injection was administered, with no oral overlap required according to the formulation characteristics.

Within 24 hours of the first injection, the patient developed a sustained and painful penile erection lasting several hours. He was urgently referred to the emergency department, where the urology team confirmed the diagnosis of acute ischemic priapism. Bilateral corporal aspiration was performed, with drainage of stagnant cavernosal blood, achieving full detumescence and symptom resolution, without immediate complications.

After stabilization, the patient remained hospitalized for continued psychiatric monitoring. Risperidone was discontinued, and treatment with olanzapine was initiated and gradually titrated to 10 mg/day. The selection of olanzapine was supported by its comparatively lower α1-adrenergic receptor affinity and by previous reports describing successful treatment with olanzapine or aripiprazole following antipsychotic-associated priapism [8]. This strategy was intended to reduce, but not eliminate, the risk of recurrence, as rare cases of olanzapine-associated priapism have been reported. The patient was counseled regarding the potential risk of recurrence and advised to seek urgent medical evaluation if symptoms recur. The new regimen was well tolerated, with no recurrence of priapism or other significant adverse events. Under olanzapine therapy, the patient maintained full remission of psychotic symptoms and clinical stability. He was discharged on oral olanzapine 10 mg/day with outpatient psychiatric follow-up arranged. Written informed consent was obtained from the patient for publication of this case report.