Methadone is similar to heroin and is also a narcotic pain reliever.Both are opioids and bind to the same receptors in the brain.All opiates are sedative drugs and one of their effects is to depress the central nervous system, they also slow down the functioning of the body and reduce both psychological and physical pain.Users experience feelings of warmth, detachment and relaxation.Methadone is longer lasting than heroin and does not produce the characteristic ‘high’ of that drug. When used in the treatment of heroin addicts it reduces the withdrawal symptoms that they experience when they attempt to come off the drug, but without the ‘high’ and is therefore often used as part of drug detoxification and maintenance programmes.

Methadone addiction has a range of effects on the body and individuals react differently to the drug. Its effect on the brain can cause mood changes, which are less intense, but longer lasting than heroin, drowsiness, nausea, slower and shallower breathing, reduced cough reflex and the reduction of physical or psychological pain.
Methadone also acts on the nerves that control involuntary functions and this usually results in pupil constriction and constipation.It can also cause reduced blood pressure, difficulty in micturition and dryness of the nose, mouth and eyes.

In some people methadone can cause the release of histamine, which leads to sweating, a feeling of itchiness, flushing of the skin and constriction of the air passageways in the lungs.Other effects can include reduced menstruation or amenorrhea, a reduced sex drive or impotence, reduced energy levels, a feeling of heaviness in the arms or legs and a craving for sweet foods.