There is actually very little data that actually supports the administration of activated charcoal (AC) to the poisoned patient. AC works by binding the toxin and preventing its absorption from the GI tract. Here are some of the practical points:
Once you have assessed your risk:benefit ratio, then administer AC. Of note, it definitely works in the right situation as noted in a landmark article that showed a decrease in mortality following poisoning by oleander - a plant that contains a digoxin like substance.(1)
1 - de Silva HA, et al. Multiple-dose activated charcoal for treatment of yellow oleander poisoning: a single-blind, randomised, placebo-controlled trial. Lancet 2003: 361(9373):1935-8.