Naltrexone Side Effects and What to Avoid
Naltrexone can cause nausea, headache, dizziness, and fatigue. Know which symptoms need prompt care, how tablet and injection risks differ, and what to discuss with the prescriber.
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Which Naltrexone Side Effects Need Attention?
Nausea, headache, dizziness, and tiredness can happen with naltrexone. If you have just started treatment, you may be wondering what to watch, what might settle, and when to call. Symptoms that are severe, persistent, or disrupting daily life deserve attention. You do not have to tolerate a problem silently to keep receiving treatment.[1]
Naltrexone tablets and the monthly Vivitrol injection share some risks, while the injection also has injection-site concerns. Side effects are only one part of safety: starting too soon after opioids and trying to overcome opioid blocking can be dangerous.[2][3]
Get emergency help for trouble breathing, facial or throat swelling, collapse, or suspected overdose. Call 911 and give naloxone for suspected opioid overdose if available. Do not assume that naltrexone prevents an overdose.[1][3]
- Commonly reported problems include nausea, headache, dizziness, sleepiness, vomiting, and changes in appetite or sleep.[1]
- An injection site that becomes very painful, increasingly swollen, blistered, or open needs prompt medical attention.[3]
- Yellow eyes or skin, dark urine, or persistent abdominal pain can be warning signs of liver injury.[3]
- Never take extra opioids to overcome naltrexone. Overdose risk also needs planning when treatment wears off or stops.[3]
Common Side Effects of Naltrexone Tablets and Injections
Naltrexone can cause an upset stomach, headache, dizziness, reduced appetite, or fatigue. Some people report vomiting, difficulty sleeping, anxiety, or muscle and joint discomfort. The frequency and pattern differ across formulations and study populations, so a percentage from one trial does not predict your individual experience.[1][2][3]
For example, the tablet label describes an open-label safety study of approximately 570 people treated for alcohol problems.[2] Newly reported nausea occurred in 10%, headache in 7%, and fatigue in 4%.[2] Because the study was open-label, those figures are reports during treatment, not proof that the medicine caused every symptom.[2]
Vivitrol trials reported many adverse reactions as mild or moderate, but some people stopped treatment because of adverse events. There is no single timetable by which everyone’s symptoms resolve. Tell the prescriber about symptoms that persist, worsen, or interfere with eating, sleeping, work, or taking the medication.[3][1]
What Can You Do About Nausea?
Let the prescriber or pharmacist know when nausea starts, whether you are vomiting, and whether you can keep fluids down. They can advise whether a change in how the medicine is taken, symptom treatment, or reassessment is appropriate. Severe vomiting or diarrhea soon after the first dose can also be precipitated withdrawal, especially after recent opioid use.[2]
Avoid treating a difficult reaction as something you must endure for a fixed number of days. The timing, severity, and other symptoms determine the response, not simply how long you have been taking naltrexone.
Does Naltrexone Make You Sleepy?
Yes, sleepiness and fatigue are recognized possible side effects. Naltrexone does not produce an opioid high, but that does not mean it cannot affect alertness. Avoid driving or operating machinery until you know how it affects you, and discuss troublesome drowsiness with the prescriber.[1][3]
Fatigue can have more than one explanation. Tell the clinician about other medications, sleep changes, mood, alcohol or other substance use, and when symptoms began. Unusual tiredness with dark urine, yellowing eyes, or persistent abdominal pain needs prompt assessment for possible liver problems rather than reassurance that you are merely adjusting.[1][3]
When to Seek Help for a Naltrexone Reaction
Describe the Change, Not Just the Symptom
“I feel tired” is a start. Add when it began, what you can no longer do comfortably, and whether it happens after a dose. Bring the medication name, tablet or injection form, last dose date, and a list of other medicines to the conversation.
The following distinctions can help you decide how urgently to respond. They do not require you to diagnose the cause before asking for help. Product labeling and SAMHSA identify serious allergic reactions, liver injury, injection-site injury, depressed mood, and opioid-related emergencies among the concerns to recognize.[1][2][3]
| What you notice | What to do |
|---|---|
| Trouble breathing, throat or facial swelling, collapse, or someone who cannot be awakened. | Call 911. For suspected opioid overdose, give naloxone if available. |
| Yellow skin or eyes, dark urine, or persistent abdominal pain. | Seek medical attention promptly. Naltrexone labeling instructs discontinuation when symptoms or signs of acute hepatitis occur. |
| Severe or worsening injection-site pain, extensive swelling, a hard area, blisters, a scab, or an open wound. | Contact the treating clinician promptly for examination. |
| Severe vomiting, diarrhea, or sudden withdrawal after starting. | Get urgent medical assessment; severe precipitated withdrawal may require hospital care. |
| Bothersome nausea, headache, dizziness, sleepiness, or other symptoms that are not improving. | Contact the prescriber or pharmacist to review symptoms and treatment. |
The warning signs and actions above come from naltrexone labeling and SAMHSA safety guidance.[2][3][1]
Injection-Site Reactions After Vivitrol
Some soreness or tenderness can occur after an injection, but worsening pain or skin changes should not be dismissed as routine. Severe reactions, including tissue injury requiring surgery, have been reported. Tell the clinician if the area is getting worse or is not improving; the injection site may need examination.[3]
Mood Changes and Thoughts of Suicide
Report new or worsening depression or suicidal thoughts promptly. Such events have been reported during treatment, although reports alone do not establish that naltrexone caused them. Monitoring and support matter regardless of the cause.[2]
In the United States, call or text 988 for suicidal distress. If there is immediate danger or a medical emergency, call 911.[4]
What to Avoid While Taking Naltrexone
Opioids need particular attention because naltrexone blocks their effects. Tell every treating clinician about naltrexone before surgery, dental treatment, or a new prescription. Some pain, cough, or diarrhea medicines contain opioids, so a pharmacist should check new products.[1]
Do not take larger opioid doses because the usual amount seems ineffective. The blockade can be overcome, and doing so can cause fatal overdose. Pain can still be treated, but the team may need nonopioid approaches or closely monitored specialist care if opioids are necessary.[2]
Naltrexone is also used in alcohol treatment, but it does not prevent intoxication or manage acute alcohol withdrawal. Discuss your drinking and treatment goals honestly. Do not use the absence of a disulfiram-like reaction as a reason to assume drinking is harmless.[2][3]
Why Recent Opioid Use Matters Before the First Dose
Naltrexone can abruptly trigger withdrawal in someone physically dependent on opioids. Labeling recommends at least 7 to 10 opioid-free days after short-acting opioids; people transitioning from methadone or buprenorphine may remain vulnerable for as long as two weeks. A clinician must assess readiness rather than relying only on a calendar.[2]
This also applies when naltrexone is prescribed for alcohol use disorder. Include tramadol and other prescribed opioids in the history you give. Severe withdrawal has occurred even after a negative test or a tolerated naloxone challenge, so there is no single test that guarantees a safe start.[3]
Naltrexone, Liver Health, and Follow-Up
The prescriber should know about liver disease, hepatitis, alcohol use, and other medications. Liver injury has been reported, sometimes with other possible contributing causes. Your medical history and symptoms guide the assessment and monitoring plan; this should not be reduced to “safe for everyone” or “never appropriate with liver disease.”[2]
Ask which tests or follow-up visits are needed and which symptoms should lead you to call sooner. The important information is what applies to your health and formulation, rather than a generic testing schedule copied from someone else’s prescription.
AddictionHelp.com · Practical resources
Discussing Naltrexone Treatment
Bring this discussion guide to the clinician who may prescribe naltrexone. Use it to compare the plan for alcohol or opioid use disorder, confirm the formulation, and prepare for safe starting and follow-up.
3-page fillable PDF · Free · No signup
Planning for Missed Doses or Stopping Naltrexone
After time without opioids, tolerance can fall. Opioid amounts that were once tolerated can cause overdose when naltrexone’s effect declines, an injection is missed, or treatment stops. Keep naloxone available and ask the prescriber what to do if you miss treatment or use opioids again.[3]
Side effects are a reason to seek a better plan, not a reason to be left without care. Use the worksheet to organize questions, compare medication options, and explore help finding treatment if you need a prescriber or additional support. The plan should address both the symptoms bothering you and the condition being treated.
Frequently Asked Questions
How Long Do Naltrexone Side Effects Last?
There is no single timetable for everyone. Tell the prescriber about symptoms that are bothersome, persistent, or worsening. Severe symptoms and warning signs should be assessed promptly instead of waiting for a set adjustment period.[1]
Can Naltrexone Affect the Liver?
Can You Take Pain Medicine With Naltrexone?
Pain can be treated, but the plan must account for opioid blocking and your other health needs. Tell the care team about naltrexone; nonopioid treatments or closely monitored specialist care may be needed. Do not increase opioids yourself.[2]
What Happens if You Use Opioids During Naltrexone Treatment?
Effects may be reduced, but overdose is still possible, especially when someone takes more to overcome blocking. Risk also changes when treatment wears off or stops because opioid tolerance can be lower.[3]
Does Naltrexone Make Drinking Alcohol Safe?
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