Paraoxon is an odorless, reddish-yellow oil. Paraoxon is an aryl dialkyl phosphate where both the alkyl groups are ethyl and the aryl group is 4-nitrophenyl. It is a cholinesterase or acetylcholinesterase (AChE) inhibitor. It is an organophosphate oxon, and the active metabolite of the insecticide parathion. Paraoxon is one of the most potent acetylcholinesterase-inhibiting insecticides available, around 70% as potent as the nerve agent sarin, and so is now rarely used as an insecticide due to the risk of poisoning to humans and other animals. Exposure to Paraoxon can cause rapid, severe organophosphate poisoning with headache, sweating, nausea and vomiting, diarrhea, loss of coordination, and death. Paraoxon is on the Hazardous Substance List because it is cited by DOT and EPA. Parathion is converted in the body in part to paraoxon, a strong inhibitor of the enzyme acetyl cholinesterase. Upon inhibition of this enzyme in the tissues, acetylcholine, the substance responsible for transmission of nerve impulses in much of the nervous system, accumulates, producing an initial overstimulation and subsequent blockage of nerve stimuli. Paraoxon was once used as an opthamological drug against glaucoma.