Methadone is a synthetic (man-made) opioid that was first synthesized in the late 1930s. Among its various uses, methadone blocks the receptors in the brain that are affected by addictive opiates such as morphine and heroin – which means that, when taken as part of an approved and medically supervised program, methadone enables addicted individuals to end their dependence upon these drugs without experiencing painful (and often dangerous) withdrawal symptoms.