An 18-year-old college freshman is transported to the emergency department following a call to EMS by his girlfriend, who found him unresponsive in his room. She reports no history of mental illness, no changes in mood, no suicidal ideation, and no hallucinations or other bizarre behavior. He doesn't use drugs, doesn't smoke, and rarely drinks. She says "I don't know what happened; he was out with his new fraternity brothers." What is the most likely diagnosis?

Choice A reason: Traumatic brain injury typically requires a history of head trauma, which is not mentioned in this case. While it can cause unresponsiveness, there is no evidence of injury or fall, making this diagnosis less likely. Choice B reason: Seizures can cause sudden loss of consciousness, but they are usually followed by postictal confusion or convulsions, which are not described here. Additionally, there is no history of epilepsy or seizure-like activity. Choice C reason: Alcohol intoxication is the most likely diagnosis given the context of fraternity involvement and sudden unresponsiveness. College initiation events often involve binge drinking, and even if the patient rarely drinks, peer pressure or hazing could lead to acute alcohol poisoning. This fits the clinical picture and social context. Choice D reason: Cardiopulmonary arrest is a critical condition, but it is a consequence rather than a diagnosis. It could result from alcohol poisoning, but without evidence of cardiac or respiratory disease, it is not the primary diagnosis.