Methadone (also known as Symoron, Dolophine, Amidone, Methadose, Physeptone, Heptadon and many other names) is a synthetic opioid. It is used medically as an analgesic and a maintenance anti-addictive and reductive preparation for use by patients with opioid dependence. It was developed in Germany in 1937, mainly because Germany required a reliable internal source of opioids. It is an acyclic analog of morphine and heroin. Methadone acts on the same opioid receptors as these drugs, and has many of the same effects. Methadone is also used in managing severe chronic pain, owing to its long duration of action, strong analgesic effect, and very low cost. Methadone is listed under Schedule I of the Single Convention On Narcotic Drugs 1961 and is regulated similarly to morphine in most countries. In the United States, it is a Schedule II Narcotic controlled substance. Methadone is mainly used in the treatment of opioid dependence. It has cross-tolerance (tolerance to similar drugs) with other opioids including heroin and morphine, and offers very similar effects but a longer duration of effect. Oral doses of methadone can stabilize patients by mitigating opioid withdrawal syndrome or making it more tolerable. Higher doses of methadone can block the euphoric effects of heroin, morphine, and similar drugs. As a result, properly dosed methadone patients can reduce or stop altogether their use of these substances.