It is derived from the opium of the poppy plant which is primarily grown in Eastern Mediterranean, Southeast Asia, and Central and South America. Heroin is made by turning the resin of the poppy into a drug called morphine. Morphine is then turned into heroin, a highly addictive narcotic.
Narcotics are excellent pain relievers and create a feeling of euphoria and a sense of well being.
The thalamus is a part of the brain which channels all the body's sensations to the brain cortex. Cells in a part of the thalamus receive messages form the body about dull, steady pain. Heroin lowers the sensitivity of these cells so that the feeling of pain is dulled or reduced. Heroin stimulates the brain cells in another part of the brain called the amygdala. This gives the user feelings of happiness and euphoria.