Drowsiness, dizziness, constipation, or headache may occur. If any of these effects persist or worsen, tell your doctor or pharmacist right away.
To prevent constipation, eat dietary fiber, drink enough water, and exercise. You may also need to take a laxative. Ask your pharmacist which type of laxative is right for you.
To reduce the risk of dizziness and lightheadedness, get up slowly when rising from a sitting or lying position.
Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.
Severe (possibly fatal) breathing problems can occur if this medication is abused, injected, or mixed with other depressants (such as alcohol, benzodiazepines including diazepam, other opioids).
Tell your doctor right away if any of these unlikely but serious side effects occur: interrupted breathing during sleep (sleep apnea), mental/mood changes (such as agitation, confusion, hallucinations), stomach/abdominal pain, signs of your adrenal glands not working well (such as unusual tiredness, weight loss).
Although this medication is used to prevent withdrawal reactions, it may rarely cause opioid withdrawal symptoms, including diarrhea, severe mental/mood changes (such as anxiety, irritability, trouble sleeping), muscle stiffness or shakiness. This is more likely when you first start treatment or if you have been using long-acting opioids such as methadone. If such symptoms occur, notify your doctor or pharmacist right away.
Get medical help right away if any of these rare but serious side effects occur: fainting, fast/irregular heartbeat, severe dizziness, slow/shallow breathing, unusual drowsiness/difficulty waking up.
This drug may rarely cause serious liver disease. Get medical help right away if you have any symptoms of liver damage, including: dark urine, loss of appetite, persistent nausea/vomiting, yellowing eyes/skin, severe stomach/abdominal pain.
A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.
This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.
In the US -
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.
In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.