Why charcoal’s surface matters
Activated charcoal is ordinary carbon processed to create an enormous network of tiny pores. That gives a small amount of it far more exposed surface than a smooth lump of the same size. When charcoal is swallowed, certain molecules in the digestive tract attach to those surfaces—a process called adsorption, in which molecules stick to a surface rather than soak into it.
If a drug or poison binds to the charcoal while it is still in the gut, less of it may cross the intestinal wall into the blood. The charcoal then travels through the digestive system and leaves the body in stool, carrying some of the bound material with it.
Why it works for some substances, not others
Adsorption depends on the chemistry of both the molecule and the charcoal. Some substances bind well; others do not. For example, charcoal generally binds many medicines, but it is poor at trapping alcohols, metals such as iron, and corrosive chemicals. It also cannot pull a substance back out of the bloodstream once the body has absorbed it.
Timing matters because the target must still be in the digestive tract. The longer a substance has had to pass into the blood, the less charcoal can intercept. Clinicians therefore consider what was swallowed, how much time has passed, and whether charcoal is appropriate; it is not a treatment to use for every poisoning.
The key is not that charcoal destroys a poison. It can reduce exposure by holding certain molecules in the gut before they enter the body’s circulation.
