Why can’t they create a drug like cocaine or heroin that retains only the positive effects (euphoria, relaxation, etc.) without causing harm and danger to health?

Question

Why can’t they create a drug like cocaine or heroin that retains only the positive effects (euphoria, relaxation, etc.) without causing harm and danger to health?

In: Chemistry

Answer 1

ELI5:

The “good parts” of drugs are normal good things your body makes, cranked up 5000%.

But if you stay at 5000%, your body adjusts to that as your new normal.

Now you need 10,000% to feel as good.

But what if you want to go back to normal? Well, you are at 5000% for so long that going back to normal now hurts, and depending on what drug, it can hurt real bad for a long time.