It is a great choice while the drugs/poisons are in your stomach or intestines (depending on where/how they are absorbed). However, after the drugs have been absorbed there isn't anything AC or any sort of anti-emetic can do to help you. Drugs don't just sit in your stomach till your done with them Depending on the make up of the chemical, you know, whether they are basic, acidic, lipophilic, or hydrophilic, the drug may be already absorbed with in an hour. Some drugs take longer, some don't take hardly any time at all.
They give anti-psychotics because it is theorized/shown that the common psychedelics in circulation are 5-ht2a receptors agonists, while anti-psychotics are antagonists, so they block the effects of the drug at the receptor. However, they don't act on all of the receptors that the psychedelics are interacting with, so you still will have effects from the drug, and a lot of the time they become unpleasant.
Benzos I'd say are the best choice as they will just calm you down and allow you to relax. They don't completely rid you off effects but they make them more bearable depending on the severity of the situation