Antidotes are therapeutic agents that counteract the toxic effects of drugs or toxins. Antidotes can exhibit their effects in several different ways. For instance, an antidote like atropine can negate the harmful effects of cholinesterase inhibitors by inactivating the muscarinic receptors and blocking excess acetylcholine from reaching the receptor site. Some enzymes that mediate biochemical pathways are inhibited by antidotes, which decrease the formation of toxic metabolites. In some cases, modified enzymes can be reactivated by antidotes, which improves enzyme function. Some antidotes can remove toxic drug metabolites by directly binding to them. Antidotes can also convert toxic metabolites into less toxic alternatives. For instance, in cyanide poisoning, sodium thiosulfate is used to accelerate the formation of thiocyanate from cyanide. The alternative metabolite formed is less toxic than cyanide and gets eliminated faster. Chelators can be used as antidotes in heavy metal poisoning, and the complexes formed are excreted in the urine.