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If I had bone cancer , or liver cancer , for example, I would be wanting access to any chronic pain medication I could get my hands on (although I'd probably be asking for fentanyl as first choice).

If the primary purpose of medicine is to reduce suffering, then I'm not sure I'd be comfortable with witholding drugs from people who need them because there's a chance they might be abused.

And if we want to extend suffering reduction to drug addicts and their families as well, then giving them access to measured doses would go a long way to helping reduce the chance of accidental overdose.

(And if you absolutely must take opiates/opioids, for heaven's sake don't get drunk at the same time, otherwise you will pass out and die from respiratory arrest...)