You're not going to want to IV K on MMT.
I was on like 1mg of buprenorphine, and I tried IV K for the first time - I remember telling myself "ok time to breathe"... and I would have to force my body to go through the mechanical motion of breathing.
You may find it too hard to breathe on such a combo.
It's going to be a K hole. If you just want sedation, pop a benzo.
IV K = psychedelic wonderland.
You're going to feel it working in seconds, seconds after you pull the needle out you will have a raging bell-ringer (I get one every time, they are more intense than IV coke bell-ringers), and within minutes you should be peaking, and tripping quite hard.
Also remember, as a recovering heroine user, ketamine is addictive, and it really "grabs" onto some people in a way completely unique to the compound.
True, I've seen people who had a really, really hard time not using ketamine...essentially impossible to stop dosing.
I didn't have a problem with ketamine, mostly because it's not something you're going to want to repeat multiple times a day for every day; it will eventually cause issues for you if you do that.
Ketamine is something I like to do every few days if it's around, if not I'm completely fine.