The large surface area of activated charcoal confers a great adsorptive capacity to this material. The adsorptive capacity of this substance differs for various chemical entities. Activated charcoal is most effective in adsorbing aromatic or benzenoid-type substances. Less well adsorbed are non-aromatic (non-benzenoid) substances, such as the various fatty acids and fatty alcohols. Inorganic substances are poorly adsorbed by activated charcoal.

Aromatic substances, such as acetaminophen, salicylates, barbiturates and tricyclic antidepressants, are very strongly adsorbed by activated charcoal, and that is why activated charcoal is commonly used in the management of overdosage of these substances. Adsorption of these drugs reduces their absorption from the gastrointestinal tract.