Every US citizen gets an electronic prescription for a terminal drug dose, one time only (associate with SSN; maybe have IRS track).
Maybe one has to be over some age to fill it. It's OK to sell it (black market) but if one does, one then only has access to 'ordinary' health care. (One round of chemo, one hip replacement, ... ) No exceptions at all for second round of prescription. Indeed some hardship. And yes, risk that teens could access these. Of course risk that people incompetent to choose would indeed choose. Yes, subject to abuse, influence. But overall, puts choice in the hands of the individual with way less risk and cost than current situation. Very American. Very autonomous. Completely simple.