Activated charcoal works to treat poisoning because it binds with some poisonous agents and helps them pass through the body without being absorbed. When activated charcoal is prescribed by a physician in this way it may be taken in several doses.
However, as a supplement, activated charcoal has not been shown to be effective in treating other conditions such as excess gas, cholesterol or hangovers. The side effects from activated charcoal include constipation and black stools. Activated charcoal may also prevent some drugs from being absorbed by the body, therefore it should not be taken at the same time as other medications.