It's been used in emergency care for decades. It's one of the most used drugs and part of the basic kit in an ambulance or ER. It's safer than other anesthetics because it doesn't affect respiration so much.

As an anesthetic sure, but what about it's effect on the brain?

The effect on the brain is that.. it's an anesthetic, not sure I follow you.

Trying to guess what you mean: it isn't used as a local anesthetic, but always on the central nervous system, causing disociation in big dosis.

For depression they use much less than that, so many decades with heavy dosage it's a very convincing safety record.

I meant as in any neurological impairment. Effects on cognitive functionality or memory retention. You know, the types of damage often reported over extended use of psychoactive drugs.

This has been much studied.

There have been a few recent papers showing brain lesions in very, very heavy recreational users, but otherwise it appears to be a very safe drug.

Can make you feel loopy and nauseous depending on amount and how quickly it goes into your body. You should go back to feeling normal again after about 10 minutes after it stops coming in. (This is based on what a friend experienced when given it by a doctor.)