 Dextromethadone (the "S" enantiomer) does not affect opioid receptors but binds to the glutamatergic NMDA ("N"-methyl--aspartate) receptor, and acts as an antagonist against glutamate.Methadone has been shown to reduce neuropathic pain in rat models, primarily through NMDA receptor antagonism.Glutamate is the primary excitatory neurotransmitter in the central nervous system.