Yeah I'm not sure it depends on your past with opioids, judging by your post I would assume this is one of your first experiences with them. I have actually never tried codeine but have heard it is very weak. The first opioid I did was half a 30mg roxy up the nose and I was LIT! I just skipped the Percocet, Vicodin, and codeine and started with straight up oxy. Be careful you are playing with fire no matter what opioid it is you try for the first time. I was pretty much in love with opiates for years because of that first 15mg of oxy I tried! From the first day I did it I never stopped until getting on subs, which aren't a whole lot better as far as opioid dependence is concerned. the withdrawls are just as bad as any other opioid, if not worse! as far as mixing herb with the codeine and percocet, I would have to say yes it will potentiate it like it does with all opioids I have tried. THC makes opioids much stronger ime. The antihistamines idk about. I used Benadryl to potentiate my bupe for a short while... but it didn't do THAT much.