Self inflicted, but why? Why in the world would anyone, no matter how crazy, want to do this when they see the results all around them?
I might suppose emotional or mental problems. Or a desire for the thrill of a high. Alcohol and drugs make you feel better, good, great, at least initially. You have problems. Maybe run of the mill, maybe horrific. And the drugs take away the bad feelings, for a while.
You become addicted, whether psychologically, physically, or both. And you start having the brain damage and physical damage that comes with the poison and the neglect of basic healthy living.
It is a tragedy but it is not a disease like say dementia. No one goes to the dealer and asks for a bag of dementia.