Psilocybin is a naturally occurring hallucinogen known to produce alterations in perception, cognition, and autonomic function through its effects on central serotonergic pathways. Products marketed as "mushroom" formulations may contain psilocybin or related psychoactive compounds despite ambiguous labeling and limited regulatory clarity, creating diagnostic challenges for clinicians in acute care settings. We present the case of an 18-year-old female with no prior medical or psychiatric history who presented to the emergency department with sudden-onset severe anxiety, agitation, tremors, diaphoresis, and vivid visual and auditory hallucinations shortly after ingesting a commercially available mushroom product purchased from a gas station. According to the patient and her boyfriend, she rapidly developed paranoid ideation and marked perceptual distortions, including the belief that her surroundings were moving and threatening her, prompting emergent evaluation. On arrival, she was tachycardic and tachypneic with dilated pupils, pronounced psychomotor agitation, and hypervigilant behavior, while remaining alert, oriented, and without focal neurologic deficits. Initial diagnostic evaluation revealed mild metabolic abnormalities without evidence of co-ingestion, pregnancy, or end-organ dysfunction, and electrocardiography demonstrated an apparent irregular rhythm initially concerning for atrial fibrillation that was subsequently determined to represent sinus rhythm with tremor-related artifact. The diagnosis of psilocybin-associated hallucinogen intoxication was reached through careful history-taking, exclusion of alternative etiologies such as primary psychosis, serotonin syndrome, or other toxic ingestions, and observation of symptom resolution with supportive care. Diagnostic uncertainty was heightened by the absence of confirmatory toxicology testing and the nonspecific labeling of the ingested product, necessitating reliance on clinical pattern recognition and response to treatment. The patient was managed with intravenous fluids and repeated doses of benzodiazepines, resulting in gradual resolution of autonomic instability, agitation, and hallucinations, and she returned to baseline mental status prior to discharge. This case highlights the diagnostic challenges posed by commercially available mushroom products and emphasizes the importance of comprehensive clinical evaluation and supportive management in suspected psilocybin intoxication. Recognition of characteristic clinical features, coupled with exclusion of dangerous mimics, remains essential for safe disposition and effective patient counseling.
