Methadone has a risk for abuse and addiction, which can lead to overdose and death. Methadone may also cause severe, possibly fatal, breathing problems and heartbeat problems. To lower your risk, your doctor should have you use the smallest dose of methadone that works, and use it for the shortest possible time. Do not increase your dose or use this medication more often than directed. See also How to Use section for more information about addiction.

Ask your doctor or pharmacist if you should have naloxone available to treat opioid overdose. Teach your family or household members about the signs of an opioid overdose and how to treat it.

The risk for severe breathing problems or heartbeat problems is higher when you start this medication, when you are switching from another opioid to methadone, after a dose increase, or if you use the wrong dose/strength. Breathing problems from methadone may not happen right away after using a dose. Most heartbeat problems have happened in people using large doses of methadone for pain relief, but this problem can also occur in people getting smaller doses to treat opioid addiction. Using this medication with alcohol or other drugs that can cause drowsiness or breathing problems may cause very serious side effects, including death. Also, other medications can affect the removal of methadone from your body, which may affect how methadone works. Be sure you know how to use methadone and what other drugs you should avoid taking with it. See also Drug Interactions section. Get medical help right away if any of these very serious side effects occur: slow/shallow breathing, unusual lightheadedness, severe drowsiness/dizziness, difficulty waking up, fast/irregular heartbeat, fainting.

Keep this medicine in a safe place to prevent theft, misuse, or abuse. If someone accidentally uses or swallows this drug, get medical help right away.

Before using this medication, women of childbearing age should talk with their doctor(s) about the risks and benefits. Pregnancy may affect the amount of this drug in your body, so tell your doctor if you are pregnant or if you plan to become pregnant. During pregnancy, this medication should be used only when clearly needed. It may slightly increase the risk of birth defects if used during the first two months of pregnancy. Also, using it for a long time or in high doses near the expected delivery date may harm the unborn baby. To lessen the risk, use the smallest effective dose for the shortest possible time. Babies born to mothers who use this drug for a long time may develop severe (possibly fatal) withdrawal symptoms. Tell the doctor right away if you notice any symptoms in your newborn baby such as crying that doesn't stop, slow/shallow breathing, irritability, shaking, vomiting, diarrhea, poor feeding, or difficulty gaining weight.