A patient is suspected of poisoning and you plan to administer activated charcoal. How long after ingestion is charcoal most effective?

• A. Only if life-threatening symptoms
• B. Within 24 hours
• C. Within 6 hours
• D. Within about 1 hour of ingestion

Answer: (D)

Activated charcoal works by adsorbing many toxins in the GI tract, preventing their absorption into the bloodstream. Its effectiveness is greatest when given soon after ingestion, while the toxin is still in the stomach or early in the small intestine. As time passes, the substance moves further along and absorption may already have occurred, so the potential benefit of charcoal drops. In EMS practice, the practical window is about within an hour of ingestion, which is why this option is the best choice. Beyond that, the benefit diminishes, though there can be exceptions for certain poisons. Airway protection and contraindications must be considered, but the key idea is that early administration yields the most adsorption of the toxin.