Heroin enters the brain quickly and binds to opioid receptors, especially those involved in feelings of pain and pleasure. These receptors also regulate heart rate, breathing, and sleeping.
Once it binds to these receptors, heroin floods the brain with dopamine, producing an intense rush of euphoria. This is often what makes heroin so addictive—the brain begins to crave that pleasurable sensation, and tolerance develops rapidly.
Over time, the brain’s reward system is rewired, making it increasingly difficult to experience pleasure from anything other than heroin. This is why many people ask, “why is heroin so addictive?”