NMDA receptor antagonists are substances that block the action of the N-methyl-D-aspartate (NMDA) receptor, a type of receptor in the brain that plays a crucial role in synaptic plasticity and memory function. By inhibiting these receptors, these antagonists can reduce excessive neuronal activity, which is often associated with conditions like epilepsy and chronic pain. These antagonists are also being studied for their potential therapeutic effects in various psychiatric disorders, including depression and schizophrenia. Some well-known NMDA receptor antagonists include ketamine and memantine, which are used in clinical settings to manage symptoms and improve patient outcomes.