Yeah i think it would actualy reduce ODs as well. At least unintentional ODs, thats usualy related to usualy having an impure product and when you have a purer product using the same amount as before. As for coverage, i think it should be covered but this coverage financed by taxing it. To the degree it actualy leads to more costs. For instance, if it has some costs but like tobacco removes primarily the last few years of your life which would otherwise be quite expensive, both should be taken into account.
Yes you can argue that not all people would let it come to any healthproblems, but in the end i think that makes the most sense. After all, espacialy if you are still young, you being more productive might in the end bring more money back in than the therapy required for that to happen. I dont think other people should have to cover that though so taxing it for that purpose makes the most sense to me.