This addictive nature of this substance is reinforced by its abilities in creating intensely pleasurable feelings. Heroin accomplishes this by binding to opioid receptors in the body. Once the chemical interaction has taken place, the affected nerve cells are prompted to release a neurotransmitter called dopamine . Dopamine is a special molecule--and important in mediating feelings of pleasure that are rewarding to the user. It's these sensations of reward that can kickstart and later reinforce a growing addiction, as the user continually seeks to repeat the behavior - in this case, heroin use - that lead to them in the first place.