Heroin is usually injected intravenously, but may also be injected intramuscularly or under the skin, smoked, or sniffed; effects last three to six hours. In some cases addicts gather in places called "shooting galleries," often located in vacant buildings, which supply the necessary paraphernalia (e.g., hypodermic needle and spoon to heat and liquefy the heroin). Sharing of heroin needles significantly increases the risk of acquiring AIDS (from contaminated blood left in the syringe). Different distributors of heroin often assign "brand names" to their products to enhance rumors of their strength ("Death Wish,""DOA") or effects ("Evening's Delight,""Magic"). Because the drug's strength and purity are unmonitored, each administration brings with it the possibility of overdose, illness from contaminants, or death. Multiple drug use involving heroin is increasingly common and results in many emergency-room visits. For example "speedballing," the use of heroin with cocaine intravenously, moderates the expected post-cocaine "crash." Instances of overdose are also increasing among the growing group of middle-class users that emerged in the 1990s as a potent powdered heroin became available.