Generic drugs are laboratory-developed products engineered to be recreational drugs or discount versions of brand-name drugs no longer protected by patents. Since the new substances have a slightly different chemical make-up, they may not be under legal control. Many are manufactured and sold illegally. Recipes for many drugs are readily available on the black market and they are usually simple to make in basement laboratories from over-the-counter drugs or other readily available precursors. The chemical structures of controlled parent substances are altered to produce compounds having properties similar to those of legal pharmaceuticals or narcotics. Examples include the family of amphetamine stimulants; ketamine ("Vitamin K"), a legal anaesthetic with effects similar to heroin; and 3-methylfantanyl, a depressant many times more potent than heroin, and mimics of the best-selling hypertensive drug diazide. Designer drugs are often more potent that the parent substances, have less stringent manufacturing and testing procedures, and can pose a serious threat to the health of the user because they may contain by-products and impurities.