Heroin, an illegal opiate drug known on the street as smack, junk, brown sugar, dope, horse, skunk and other names is derived from the resin of the poppy plant which grows predominantly in southeast and southwest Asia, Mexico and now in Colombia. It is manufactured in remote laboratories using rudimentary equipment which presses the powder into bricks for bulk shipment to destination countries like the United States. Smaller amounts are smuggled by couriers who swallow heroin-filled latex balloons before boarding commercial airlines.

Pure heroin is a white powder with a bitter taste. Most illicit heroin is a powder form which may vary in color from white to dark brown because of impurities left from the manufacturing process or the presence of additives. Pure heroin is rarely sold on the street. A "bag" (slang for a single dosage unit of heroin) may contain 100 mg of powder, only a small portion of which is heroin. The remainder could be sugars, starch, powdered milk, or quinine. Traditionally the purity of heroin in a "bag" has ranged from one to ten percent. More recently, heroin purity has ranged from one to ninety-eight percent, with a national average of thirty-five percent.

Another form of heroin, "black tar," has also become increasingly available in the western United States. The color and consistency of black tar heroin results from the crude processing methods used to illicitly manufacture the substance in Mexico. Black tar heroin may be sticky, like roofing tar or hard like coal, and its color may vary from dark brown to black. It is often sold on the street in its tar-like state at purities ranging from twenty to eighty percent. This heroin is most frequently dissolved, diluted and injected.

The typical heroin user today consumes more heroin than a typical user did just a decade ago, which is not surprising given the higher purity currently available at the street level. Until recently, heroin in the United States almost exclusively was injected either intravenously, subcutaneous (skin-popping), or intramuscularly. Injection is the most practical and efficient way to administer low-purity heroin. The availability of higher purity heroin has meant that users now can snort or smoke the narcotic. Evidence suggests that heroin snorting is widespread or increasing in those areas of the country where high-purity heroin is available, generally in the northeastern United States. This method of administration may be more appealing to new users because it eliminates both the fear of acquiring syringe-borne diseases such as HIV/AIDS and hepatitis, and the historical stigma attached to intravenous heroin use.