[joefigura]

A person who becomes addicted to opiods, methamphetamine, or other "hard" drugs will with some probability require medical treatment, and and some people who uses those drugs will cause other costs to society. I don't know what those percentages are, but for opiods it's definitely not negligible. Many people begin using opiods and become addicted without intending to, and later need medical assistance. So there is a public interest in how much these substances are used, and it's legitimate for government to regulate them.

In other words, there's a tradeoff between the autonomy to do things to your body and the real costs that drug addiction imposes on others.