Adults should have the legal right to poison themselves. They should not have the legal authority to stop other adults from self poisoning.
Agreed, IMO, to believe otherwise would negate the premise of self ownership. In other words, if one starts with the premise that we own our bodies (which seems self evident), then it follows that only we can choose what we do with it. For others to place these restrictions puts some sort of claim of ownership over our bodies, which runs contrary to our conscious experiences. (it also follows that anything produced by the fruits of our bodies is entirely our own too, but that’s off subject) :)
Everyone has the right to commit suicide. However, that doesn’t mean that the government doesn’t have the right to make certain suicidal behaviors illegal for reasons of public interest. If heroin were legal for adults and were no longer an “outlaw” substance, more children would gain access to it and try it.