I haven't tried it but read that it is given in injections somehow. I don't believe it's made for long time use yet.
I've had bad results with prescribed antidepressants and tried most of them. Now I've been using the supplement 5htp. I get the Puritan's Pride brand and take 200 mg. a day. I began to notice the difference after about 3 weeks. I started at 100 mg. a day then upped it to 200 after a week. It seems to help even though I still have some pretty bad days.
Patients can get a four day ketamine infusion in hospital here for severe depression or chronic nerve pain. It gives them a break when they can't stand another minute of reality. It makes sense I suppose.
'Here' is the Netherlands, btw.