Manufacture and supply
90% of the world’s heroin comes from opium grown in just a few provinces in Afghanistan. Although purer heroin is becoming more common, most street heroin is "cut" with other drugs or with substances such as sugar, starch, and powdered milk.
Street heroin can also be cut with strychnine or other poisons. Because heroin users do not know the actual strength of the drug or its true contents, they are at risk of overdose or death.