''Heroin comes in various forms, but pure heroin is a white powder with a bitter taste. Most illicit heroin comes in powder form in colors ranging from white to dark brown...Users tend to report feeling a “rush” or a surge of pleasurable sensations.''
''Heroin releases an excess of dopamine in the body and causes users to need an opiate continuously occupying the opioid receptor in the brain. Methadone occupies this receptor and is the stabilizing factor that permits addicts on methadone...''PDF format
This web site has good information about heroin. The topics include: What is heroin? - What does it look like? - Who uses heroin? - How is heroin abused? - What are the risks? - What is it called? - Is heroin illegal?