After cold turkey off 300 mg oxycodone plus morphine, MY experience is kratom withdraw is a non-event. I had mildly achy limbs, was cranky, and had insomnia. With oxycodone, I had horrific nausea, vomiting, diarrhea, muscle pain like I got hit by a fucking truck, tachycardia and severe, endless insomnia and anxiety. Wished for death. In my experience, a slow taper plus spread the dose interval out and one can step off kratom quite easily. Hopefully it will be your experience.
I have used kratom in between refills for almost 2 years. I never had a weight gain issue. I wasn't using Benadryl until I stepped completely off the oxycodone. It did help with the nausea I get. Who knows! It will be cool to see what happens but I can tell you for sure my appetite is much less off the antihistamine. Do a search on medications that cause weight gain. Benadryl tops the list.