NMDA Receptor Antagonist (NMDAR): An NMDA receptor antagonist is a drug that reduces excessive or pathological nerve cell activity that’s linked to various neurological and psychiatric conditions. NMDA stands for N-methyl-D-aspartate, a receptorchannel—a glutamate receptor in the central nervous system, primarily located on nerve cells or neurons. Glutamate is the brain’s main excitatory neurotransmitter. NMDAR plays a critical role in synaptic plasticity (ability of synapses to strengthen or weaken over time, which is the cellular basis for learning and memory), neuronal health (normal synaptic activity through NMDAR is essential for maintaining healthy brain function), and calcium ion influx (allowing positively charged ions to flow into the neuron). Many clinically used antagonists, such as memantine and ketamine, enter and block the prolonged, excessive activity associated with conditions like Alzheimer’s disease or chronic pain, while allowing normal synaptic transmission to occur. NMDA receptor antagonists are used to treat various conditions: 

• Anesthesia: Drugs like ketamine and nitrous oxide are used to induce dissociative anesthesia.
• Depression: Ketamine and esketamine have been shown to produce rapid antidepressant effects, particularly in treatment-resistant depression.
• Pain management: Certain antagonists, like ketamine and dextromethorphan (a common cough medicine ingredient), are used to manage neuropathic and chronic pain.
• Alzheimer’s and Parkinson’s diseases: Memantine is used to manage Alzheimer’s symptoms by protecting neurons from damage caused by excess glutamate activity. Amantadine is an NMDA antagonist used to treat Parkinson’s disease. 
• Some NMDA antagonists, such as phencyclidine (PCP) and ketamine, are also used recreationally for their dissociative and hallucinogenic properties