Heroin

Other effects

Receptors for endorphins and morphine are found in a number of places in the brain. These can explain several specific effects of heroin.

Eye pupils
Several areas in the brain regulate the pupillary opening in the eye. These areas contain many receptors for endorphins and opiates. That explains why heroin contracts the pupils to the size of pinheads.

Bowels
The gastro-intestinal system also contains a large number of opioid receptors. Heroin inhibits bowel activity. Heroin addicts often suffer constipation (in the past, opium was used to control diarrhoea).

Vomiting
Heroin stimulates the vomiting centre in the brain. When people take opiates, they often experience nausea and vomiting, especially in the beginning.

Coughing
Heroin suppresses the cough centre in the brain. This why other opiates (like codeine) are used in coughing syrup.