 The dextrorotary form (dextromethadone), which acts as an NMDA receptor antagonist and is devoid of opioid activity, has been shown to produce analgesia in experimental models of chronic pain.Methadone also acted as a potent, noncompetitive α3β4 neuronal nicotinic acetylcholine receptor antagonist in rat receptors, expressed in human embryonic kidney cell lines.Methadone has a slow metabolism and very high fat solubility, making it longer lasting than morphine-based drugs.