I'll be honest—I don't really understand what you're trying to achieve here.
You're asking for something excruciatingly painful, long, with a 50% chance of death, but no external physical damage and no risk of permanent disability? That's a contradiction in terms. Most things that cause intense, prolonged pain and have only a partial lethality rate are incredibly risky in the worst ways: they often leave people alive with organ damage, nerve damage, or long term suffering—not in some cinematic "coin flip" scenario, but in months or years of medical hell. Especially when it comes to pills.
Overdoses of things like NSAIDs, paracetamol, antidepressants, or common household drugs often fail to kill, but succeed in causing irreversible liver or kidney failure, seizures, or chronic illness. These aren't graceful exits. They're ER beds, feeding tubes, and a lifetime of complications if you survive. And your chances of being "physically untouched" after a failed attempt are slim to none.
I'm not trying to moralise—I'm pro-choice in the sense that I believe people have the right to decide—but I also believe people deserve to understand what they're asking for. This isn't flipping a coin. It's spinning a roulette wheel where the outcomes are rarely death or survival. They're often something far worse in between.
If what you're looking for is clarity or control over the end, I'd strongly urge you to re-evaluate whether pain, ambiguity, and risk are actually aligned with that goal or if they're a reflection of something else entirely.