[throwaway5752]

That's just not true. One habituates to it and they need more to achieve the same feeling that they had before. They need more, and the dynamic changes from trying to stay high to trying to avoid withdrawal. They reach a crisis, and then either die or go clean for a while. It changes the function of your brain, and you remain at a high risk for relapse the rest of your life (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5046044/ and countless others). There is a reason the disease model works and health system vs criminal system has better outcomes.

It eats you from the inside because everything else in life fall away in importance of being high, and if manage to get clean you are essential on a tightrope the rest of your life and the temptation haunts you all the time. It ruins your ability to feel truly happy or fulfilled by anything besides heroin. You are a day or two away from the morgue the rest of your life.

The addiction cycle usually ends in a place where Hep, sepsis, and HIV are comorbidities. But the long term health effect is the addiction and brain structural changes. Just because it's mental health doesn't mean it's any less real than lung cancer or cirrhosis.