 NMDA receptors have a very important role in modulating long-term excitation and memory formation.NMDA antagonists such as dextromethorphan (DXM, a cough suppressant), ketamine (a dissociative anaesthetic), tiletamine (a veterinary anaesthetic) and ibogaine (from the African tree "Tabernanthe iboga") are being studied for their role in decreasing the development of tolerance to opioids and as possible for eliminating addiction/tolerance/withdrawal, possibly by disrupting memory circuitry.Acting as an NMDA antagonist may be one mechanism by which methadone decreases craving for opioids and tolerance, and has been proposed as a possible mechanism for its distinguished efficacy regarding the treatment of neuropathic pain.