Black tar heroin is a form of heroin that is sticky like tar or hard like coal. Its dark color is the result of crude processing methods that leave behind impurities. Despite its name, black tar heroin can also be dark orange or dark brown in appearance.

Black tar heroin is impure diacetylmorphine. Other forms of heroin require additional steps of purification post acetylation. With black tar, the product's processing stops immediately after acetylation. Its unique consistency however is due to acetylation without a reflux apparatus. As in homebake heroin in Australia and New Zealand the crude acetylation results in a gooey mass.

Black tar as a type holds a variable admixture of morphine derivatives—predominantly 6-MAM (6-monoacetylmorphine), which is another result of crude acetylation. The lack of proper reflux during acetylation fails to remove much of the moisture retained in the acetylating agent, glacial acetic acid.

Black tar heroin is often produced in Latin America, and is most commonly found in the western and southern parts of the United States, while also being occasionally found in Western Africa. It has a varying consistency depending on manufacturing methods, cutting agents, and moisture levels, from tarry goo in the unrefined form to a uniform, light-brown powder when further processed and cut with lactose.