AM404, also known as N-arachidonoylaminophenol, is an active metabolite of paracetamol (acetaminophen), responsible for all or part of its analgesic action. Chemically, it is the amide formed from 4-aminophenol and arachidonic acid.
AM404 was originally reported to be an endogenous cannabinoid reuptake inhibitor, preventing the transport of anandamide and other related compounds back from the synaptic cleft, much in the same way that common selective serotonin reuptake inhibitor (SSRI) antidepressants prevent the reuptake of serotonin. Earlier work on the mechanism of AM404 suggested that the inhibition of fatty acid amide hydrolase (FAAH) by AM404 was responsible for all of its attributed reuptake properties, since intracellular FAAH hydrolysis of anandamide changes the intra/extracellular anandamide equilibrium. However, this is not the case, as newer research on FAAH knockout mice has found that brain cells internalize anandamide through a selective transport mechanism which is independent of FAAH activity. This mechanism is inhibited by AM404.
AM404 is also a TRPV1 agonist and inhibitor of cyclooxygenase COX-1 and COX-2, thus attenuating prostaglandin synthesis. AM404 is thought to induce its analgesic action through its activity on the endocannabinoid, COX, and TRPV systems, all of which are present in pain and thermoregulatory pathways.