People are not forced to self-medicate and their ailments are adequately treated. This also accounts for life expectancy differences unrelated to drugs. People can't get adequate health care for any number of conditions and those conditions are made worse by poverty and lack of other resources. So they die instead. Maybe with drugs, maybe by suicide or just by not treating whatever else is wrong with them.

And it is also due to our puritanical treatment of addicts. This is a medical condition, not a criminal one, so harm reduction should be the order of the day. And the treatment for addiction is unavailable for a lot of people who want help.