context: Methadone is part of a category called opioids. It was created by German doctors during World War II. When it arrived in the United States, it was used to treat people with extreme pain. Today, your doctor may use it as part of your treatment for an addiction to heroin or narcotic painkillers. It works a lot like morphine does. You can take it as a tablet, a powder, or a liquid. It must be prescribed by a doctor. People who take it illegally often inject it, which exposes them to diseases like HIV. Even though it's safer than some other narcotics, your doctor should keep a close watch on you while you take methadone. Taking it can lead to addiction or abuse. Methadone changes the way your brain and nervous system respond to pain so that you feel relief. Its effects are slower than those of other strong painkillers like morphine. It blocks the high you get from drugs like codeine, heroin, hydrocodone, morphine, and oxycodone. Your doctor may prescribe methadone if you're in a lot of pain from an injury, surgery, or chronic illness. It can also help if you're in treatment for addiction to other opioids. It can give a similar feeling and prevent withdrawal symptoms. You may hear this called replacement therapy. Methadone replaces the opioids in your system with milder effects. It's usually used as one part of your treatment plan. It isn't a cure for addiction. While there's no set amount of time you'll take methadone to treat an addiction, experts say it should be at least a year, and maybe more than that. The doctor will carefully track your body's response to it and adjust your treatment. When it's time to stop taking it, he'll help you stop slowly to prevent withdrawal. With short-term use, you may notice: Restlessness Nausea or vomiting Slow breathing Itchy skin Heavy sweating Constipation Sexual problems Some side effects are more serious. Call the doctor if you: Have trouble breathing or can only take shallow breaths Feel lightheaded or faint Get hives or a rash Have swollen lips, tongue, throat, or face Have chest pain or a rapid heartbeat Have hallucinations or feel confused If you use the drug for a long time, it might lead to lung and breathing problems. It can also change a woman's menstrual cycle. If you get pregnant, talk to your doctor about changing your dose. It can cause complications. Some people shouldn't take methadone. Tell your doctor if you have: Heart disease A heart rhythm disorder An electrolyte imbalance Breathing problems or lung disease A history of head injury, brain tumor, or seizures Liver or kidney disease Problems urinating Gallbladder, pancreas, or thyroid problems A condition for which you take sedatives Drugs than can affect methadone include: Other narcotics Drugs that make you sleepy or slow your breathing Drugs that change your serotonin level You can become dependent on it. Your brain may begin to rely on the pain relief it brings. Even though the effects are milder than other opioids, your body can still adapt to it. This means that you'll need to take more to feel the same relief from pain or withdrawal symptoms, which can lead to abuse and addiction. Your doctor will call this tolerance. No two people react the same to methadone. Your doctor calculates the dose that's right for you. Changing it can lead to dangerous side effects or an overdose. Overdose symptoms can include: Slow breathing Slow heart rate Severe drowsiness Weak muscles Cold, clammy skin Small pupils Fainting In some cases, overdose can be fatal. It's important to be honest with your doctor about your methadone use.