If a person collapses and is unresponsive with no pulse, what is the likely cause?

When a person collapses and is unresponsive with no pulse, the most likely cause is sudden cardiac arrest. This condition occurs when the heart suddenly stops pumping blood effectively, which can result from various issues, including coronary artery disease, arrhythmias, or other heart-related conditions.

In sudden cardiac arrest, the individual may not show warning signs before collapsing, and immediate action, such as CPR and defibrillation, is crucial to improve the chances of survival. The absence of a pulse indicates that blood is not being circulated, preventing oxygen from reaching vital organs, including the brain.

While the other options, such as a severe allergic reaction, drug overdose, and stroke, can lead to serious health emergencies, they typically present with additional signs or symptoms before the state of unresponsiveness and lack of pulse occur. For instance, an allergic reaction may show signs like swelling or difficulty breathing, a drug overdose might involve other symptoms like lethargy or abnormal breathing, and a stroke can manifest with sudden weakness, speech difficulties, or alterations in vision. Therefore, in the scenario described, sudden cardiac arrest is the most plausible and immediate concern requiring urgent intervention.