system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5-The mechanism by which, as we currently understand it, Ketamine produces such remarkable antidepressant effects?
gpt
We don't know. If we knew the mechanism, we wouldn't need to screw around with ketamine, we could just find or produce a molecule with similar properties. 

Ketamine is a compound in a class called NMDA receptor antagonists - it blocks the activity of a complex protein called an NMDA receptor. These receptors allow electrical activity to pass between the brain and the spinal cord. 

The effect of NMDA receptor antagonists is, in general, anesthetic. Ketamine produces what is known as "dissociative anesthesia". This means that in addition to reducing or eliminating the sensation of pain, it also "dissociates" the patient from their environment - the patient no longer feels connected to the world around them. 

Speculation has it that this dissociative effect gives the brain a chance to unwind itself when depression sets in. Depression tends to be a self-reinforcing condition. The more depressed you are, the more depressed you are likely to be in the future. Because Ketamine disconnects the cognitive areas of the mind from the rest of the brain, it may short circuit this cycle.

But, again, we simply don't know for sure. Ketamine and other hallucinogens have been historically difficult to conduct research on, owing to the stigma associated with them. Early research indicates that Ketamine could be a very powerful antidepressant. More importantly, it seems to cut short a patient's suicidal thoughts. Plus it has a very rapid effect onset - SSRIs take weeks to get to therapeutic levels. So research is probably going to pick up.