Smoking, drug addiction, alcoholism are all terrible for your health, but people often persist in their ways even after they are starting to have serious problems.
A firefighter friend of ours told us he sometimes gets calls for people who have emphysema and are on oxygen in their homes, but still smoke. They'll call 911 frantically trying to explain how they can't breathe. The crew will arrive at the house to find it stinking of cigarette smoke. He also told us a couple of times he responded to calls where someone who was on oxygen and smoking set themselves and their houses on fire.
I used to smoke. I quit ten months ago after 20 years and sometimes I feel so stupid that I did that for so long. What got me to quit was a co-worker who was 52 and told me he had emphysema. He still smokes.
I have a friend who has lost most of his other friends and most of his family because he's a drunk. The last time I talked to him he had a long weekend and told me he drank 72 beers in that time. He's one of those alcoholics that has to drink or suffer severe withdrawal. I've known him for over 20 years and he has been an alcoholic for at least 15 years. He's lost almost everything and can't hold down a job. He's almost 40 and still lives with his mom because he can't support himself. But he continues to drink no matter what anyone says to him.
In short, there's probably not much you can personally do to change their behavior. You can patch them up and tell them not to do it again, but they will continue on the path of self-destruction until they change on their own or die an early death.