Heroin is an addictive substance that comes from morphine. Although pharmaceutical companies make morphine from the seeds of poppy plants, heroin isn’t a regulated drug like morphine. Poppy plants are the source of opium, which is used to make both heroin and morphine.

As a strong opiate, heroin has an intense effect on the reward system in the brain. It increases the production of dopamine, a naturally created chemical by the brain. However, when heroin is introduced into the body by the addict, the brain stops naturally making its own. With a structure similar to endorphins, another chemical in the body, heroin also reduces the perception of pain. Heroin enters the brain rapidly and changes back into morphine. It binds to opioid receptors on cells located in many areas of the brain, especially those involved in feelings of pain and pleasure. Opioid receptors are also located in the brain stem, which controls important processes, such as blood pressure, arousal, and breathing.

The effect on dopamine production, however, is what makes heroin so addictive. The brain becomes accustomed to the high chemical levels and can’t function without heroin anymore. The association in the brain that heroin is a reward, along with the physical withdrawal, is why users find it difficult to quit without help.