Erectile Dysfunction Drug Linked to Rare Acute Psychiatric Syndrome in Case Report

A single dose of one of the world’s most familiar medications may have triggered a dramatic and unsettling psychiatric breakdown in a previously healthy man, according to a case report published in BMC Psychiatry. The drug in question is sildenafil, the phosphodiesterase type 5 inhibitor better known by its original brand name, Viagra, and taken by millions of men worldwide for erectile dysfunction. Clinicians at the Mental Health Center of West China Hospital, Sichuan University, describe a 45-year-old patient with no prior psychiatric history who developed a striking constellation of symptoms after taking the drug: cognitive impairment, unstable and mixed mood states, behavioral disinhibition, and hypersexuality. The case is unusual not merely because a neuropsychiatric reaction occurred, but because of how thoroughly the team documented it, including a positive rechallenge in which symptoms returned when the drug was taken again, a pattern that substantially strengthens causal inference in pharmacovigilance.

Sildenafil’s mechanism of action is well characterized in the vascular system, which is precisely why its potential to disturb the brain is easy to overlook. The drug selectively inhibits phosphodiesterase type 5, an enzyme that degrades cyclic guanosine monophosphate, or cGMP. When nitric oxide is released during sexual arousal, cGMP signaling relaxes smooth muscle in the corpora cavernosa of the penis, increasing blood flow and enabling an erection. By blocking cGMP breakdown, sildenafil amplifies and prolongs this pathway. But phosphodiesterase enzymes and nitric oxide signaling are not confined to the pelvis. Nitric oxide synthase is expressed throughout the central nervous system, and cGMP-dependent signaling, including the protein kinase G pathway, participates in neuronal excitability, synaptic plasticity, and vascular regulation within the brain. The report’s authors note that these pathways, together with possible effects on the serotonin transporter, offer plausible biological routes by which a PDE5 inhibitor could, in susceptible individuals, destabilize mood, cognition, and impulse control.

For most users, sildenafil is benign. Headache, facial flushing, dyspepsia, and nasal congestion dominate its side-effect profile, and these are typically mild and transient. Rare neuropsychiatric events, however, have surfaced sporadically in the literature and in spontaneous reporting systems over the decades since the drug’s approval: isolated cases of psychosis, agitation, mood disturbance, and amnesia. What makes the new report distinctive, the authors argue, is the specific combination of deficits it documents. Cognitive impairment, affective instability, disinhibition, and hypersexuality appearing together as an acute syndrome in a patient with a clean psychiatric history has, to their knowledge, been described only very rarely in connection with sildenafil exposure. That combination suggests involvement of multiple neural systems at once, including frontal networks that govern impulse control and sexual behavior, and temporal or subcortical circuits implicated in affect regulation and memory.

The clinical course described in the report followed a pattern that drug-safety specialists find particularly persuasive. The patient’s symptoms emerged acutely after sildenafil use, an abrupt onset inconsistent with the gradual evolution typical of primary psychotic or mood disorders. When the drug was discontinued, the syndrome partially remitted, a dechallenge response consistent with a pharmacological trigger. When the patient was re-exposed, the symptoms recurred, providing a natural experiment that few case reports can offer. Finally, with strict avoidance of sildenafil and a course of antipsychotic treatment, the patient made a full recovery. The authors applied structured causality assessment, referencing the World Health Organization Uppsala Monitoring Centre criteria, and report strong causality scores, placing this case among the more rigorously substantiated examples of a PDE5 inhibitor-associated psychiatric reaction in the literature.

Diagnostic rigor was central to the workup, because acute neuropsychiatric change in a middle-aged adult demands the exclusion of far more common and dangerous causes. The abbreviation list of the paper hints at the breadth of investigations undertaken: computed tomography and magnetic resonance imaging of the brain, electroencephalography, cerebrospinal fluid analysis, screening for human immunodeficiency virus, next-generation sequencing, and intravenous immunoglobulin considered in the differential. Structured instruments were used to quantify the psychiatric picture, including the Brief Psychiatric Rating Scale, the Young Mania Rating Scale, the Hamilton Depression and Anxiety Rating Scales, the Hypomania Checklist-32, the Montreal Cognitive Assessment, the Chinese Mini-Mental Status examination, and the Confusion Assessment Method. This systematic approach allowed the team to rule out structural lesions, autoimmune and infectious encephalitides, and neurodegenerative disease before attributing the syndrome to the drug, and it illustrates the standard of evidence that credible case reports must meet.

Why might sildenafil, of all drugs, occasionally provoke such reactions? Several mechanisms have been proposed across the pharmacological literature, and the report situates its case within this debate. One hypothesis centers on hemodynamics: PDE5 inhibition can alter cerebral blood flow, and changes in vascular tone might perturb vulnerable neural circuits. Another involves the cGMP and protein kinase G pathways themselves, which modulate neurotransmitter release and neuronal firing; excessive potentiation of these signals could theoretically shift the balance of excitation and inhibition in regions such as the prefrontal cortex and limbic system. A third possibility implicates serotonergic signaling, since some evidence links PDE5 inhibition to changes in serotonin transporter function, and serotonergic dysregulation is a common thread in disorders of mood and impulse control. Genetic variation in any of these pathways could explain why the overwhelming majority of users tolerate the drug while a vanishingly small subset develops florid symptoms.

The epidemiological context is what gives the case its public-health edge. Sildenafil and its chemical cousins, tadalafil and vardenafil, are among the most widely consumed prescription medications on earth, and a growing share of sales flows through online pharmacies where men obtain the drugs without medical supervision, without screening for contraindications, and without any systematic follow-up for adverse effects. In that environment, a rare neuropsychiatric reaction is unlikely to be recognized for what it is. A man who becomes acutely paranoid, disinhibited, or sexually compulsive after buying sildenafil online is more likely to be brought to an emergency department as a psychiatric emergency than to have the temporal link with the drug identified. Cases like this one serve as a reminder to front-line clinicians that a careful medication history, including over-the-counter and internet-purchased drugs, is an indispensable diagnostic tool.

The authors’ central message is directed at their colleagues in psychiatry, neurology, and primary care: maintain a high index of suspicion for drug-induced etiologies when patients present with acute, atypical psychiatric symptoms. The practical implications are concrete. When a neuropsychiatric syndrome arises shortly after starting a new medication, the medication should be stopped and the patient observed for remission; rechallenge should generally be avoided precisely because it carries risk, and in this case it occurred and reproduced the illness. Symptomatic treatment with antipsychotic medication, combined with strict avoidance of the offending agent, led to full resolution here, suggesting that the syndrome is reversible when recognized early. The case also underscores the value of standardized causality instruments, such as the WHO UMC criteria, in transforming anecdote into evidence.

It bears emphasizing that a single case report cannot establish how often such reactions occur, nor can it identify which patients are at risk. Millions of doses are taken safely, and the absolute risk of a severe neuropsychiatric event appears to be extraordinarily low. The value of the report lies in expanding the recognized spectrum of PDE5 inhibitor adverse effects and in demonstrating, with dechallenge, rechallenge, and structured causality scoring, that the association can be more than coincidence. For researchers, it opens questions about nitric oxide signaling in the brain that are worth pursuing with formal epidemiological and mechanistic studies. For the public, the takeaway is measured rather than alarming: sildenafil remains a well-tolerated and effective treatment for erectile dysfunction when used appropriately under medical supervision, but anyone who experiences abrupt changes in mood, thinking, or self-control after taking it should seek medical attention promptly and mention the drug explicitly. In pharmacovigilance, as this case shows, the rarest reactions often teach the sharpest lessons.

Subject of Research: Sildenafil-induced acute neuropsychiatric syndrome in a patient without prior psychiatric history

Article Title: Sildenafil-induced acute neuropsychiatric manifestations with cognitive impairment, affective instability, disinhibition, and hypersexuality: a case report

Article References: Song, B., Yuan, Y., Li, F., Li, Z., Yang, X., & Li, Z. (2026). Sildenafil-induced acute neuropsychiatric manifestations with cognitive impairment, affective instability, disinhibition, and hypersexuality: a case report. BMC Psychiatry. https://doi.org/10.1186/s12888-026-08703-9

Image Credits: AI Generated

DOI: 10.1186/s12888-026-08703-9

Keywords: sildenafil, PDE5 inhibitor, neuropsychiatric adverse effects, case report, erectile dysfunction, cognitive impairment, disinhibition, hypersexuality, affective instability, pharmacovigilance, BMC Psychiatry, drug-induced psychosis