We really do and do not understand how these NMDA receptor drugs work in how they treat Depression. Certain NMDA receptor agonist drugs work and certain ones do not in animal and human testing so we know it is related to NMDA but it is more complicated than that for other systems are involved (NMDA / Glutamate receptors are one of the most common receptor in the brain and Glutamate is the most common neurotransmitter.) But the fact we are figuring out certain NMDA drugs work and certain ones do not is a good sign.

Another drug Rapastinel that is a NMDA is in Phase 3 trials for Depression and it also has benefits for suicidal thoughts. It got breakthrough testing prior to Ketamine but it is about a year behind due to it taking longer to get its currently being done Phase 3 trial underway.

The same drug maker (Allergan previously Naure who is doing Rapastinel has also discovered a stronger and more effective in trials agents with Apimostinel, they took the Rapastinel molecule and modified it adding a benzyl group on the molecule. This new agent Apimostinel is current in Phase 2 trials.

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And there are numerous more drugs for depression in Phase 2 and Phase 3 FDA trials. It is just the NMDA and the Opiate / Endorphin drugs that are exciting for they treat depression in ways completely different than the monoamine systems.

We are also looking into immune modulating drugs for we noticed certain cytokines (immune modifying chemicals) where if you have higher levels of various specific cytokines it modifies response to SSRI therapy. I find this ironic for I know my specific autoimmune condition is treated by one of these medicines (a medicine I can not afford due to cost, it is extremely expensive.) But yeah medical experts are hoping that combination medicine may be beneficial may be helpful for attacking the problem via multiple vectors, using an adjunct to traditional antidepressants.