One problem that you seem to not have considered is reliability. When you buy an opioid, you have no way of knowing how much you will be getting at one time. Say you buy a bit of cocaine and it's laced with an opioid, how are you going to be sure it has enough in it to CTB? What if there is just enough to get you addicted and not enough for you to CTB? Then you're addicted and NEEDING even more and more each day just to feel "normal"... sounds like a bigger problem than what you had that may have caused you to want to CTB in the first place, now you've got your original problem PLUS you're addicted to an opioid!!!