Heroin is the diacetyl derivative of morphine. It is not available in the United States for therapeutic use, al-though its use as a recreational drug is again on the rise. It is either injected or snorted (taken intranasally). It is most often cut, or diluted, with substances such as qui-nine, which contribute to the flash, or high. Injection of the drug leads to the eventual collapse of the vessels into which it is injected, leading to the appearance of track marks under the skin. Heroin passes rapidly into the brain and thus has a rapid onset of action. It is then metabolized to morphine. The rapid onset contributes to the abuse liability of the drug. Heroin use in pregnant women can lead to low-birth-weight babies, babies born addicted to heroin, immunosuppression, and an in-creased incidence of infections in both the mother and newborn; an increased incidence of AIDS also occurs.