There is emotional pain and then there is physiological pain.
Drugs and alcohol alleviate emotional pain and have physilogical "pleasure" effects in some cases. But most of the negative effects that are frequently talked about are physiological.
Apples shouldn't be compared to oranges. A good comparison would for example be to compare the pleasures of drugs against the emotional toll caused by the negative sociological effects (can't get jobs,stigma,less friends in some cases,unintended harm to loved ones,etc...)
People take medical drugs like anti-depressants all the time knowing full well long term use can have side effects and even in the short term there can be severe side effects.