What happens if I take opioids while on naltrexone?

Naltrexone blocks opioid receptors, so opioids will not produce their usual effect. However, taking large amounts of opioids trying to overcome the block can cause dangerous or fatal overdose.

Can naltrexone cause withdrawal?

In opioid-dependent individuals who have not completed the washout period, naltrexone can precipitate sudden, severe withdrawal. For alcohol use disorder, no washout is needed.

Does naltrexone work for alcoholism?

Yes. Clinical trials show naltrexone reduces heavy drinking days by about 25% and helps people maintain abstinence or significantly reduce consumption, especially when combined with counseling.

Is the injection better than the pill?

Vivitrol (monthly injection) has the advantage of guaranteed adherence for a full month. Oral naltrexone requires daily dosing discipline. Your doctor can help determine which is right for you.

What to Expect When Starting Naltrexone

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Introduction

Naltrexone (ReVia, Vivitrol) is an opioid receptor antagonist used to support treatment of alcohol use disorder (AUD) and opioid use disorder (OUD). For OUD, the patient must be completely opioid-free for at least 7-10 days before starting to avoid precipitated withdrawal. For AUD, no opioid washout is needed. Naltrexone reduces the rewarding effects of alcohol and opioids and helps reduce cravings.

Week-by-week timeline

Before Starting

Opioid-Free Period (for OUD)

If starting for opioid use disorder, you must be completely opioid-free for at least 7-10 days (14 days for methadone). A naloxone challenge test may be performed to confirm opioid-free status before the first dose.

Week 1

Initiating Treatment

For oral naltrexone, treatment starts at 25-50 mg daily. Common early side effects include nausea, headache, anxiety, and fatigue. Nausea is most common in the first 1-2 weeks and improves. Take with food to reduce nausea.

Weeks 2-4

Craving Reduction

Cravings for alcohol or opioids typically begin to reduce. For alcohol use disorder, some patients use the Sinclair Method (taking naltrexone before drinking). Naltrexone does not make you sick from alcohol — it reduces the pleasure and reinforcement.

Weeks 4-8

Building Behavioral Change

Naltrexone works best alongside counseling and behavioral therapies. Medication compliance is critical — the oral form requires daily adherence. The monthly injection (Vivitrol) eliminates the need for daily dosing.

Month 3+

Sustained Recovery Support

Naltrexone is effective for at least 6-12 months as part of a comprehensive treatment plan. Regular monitoring of liver function is recommended. Long-term use is safe for most patients.

When to call your doctor

Contact your healthcare provider if you experience:

If you use opioids while on naltrexone: tell emergency responders you are on naltrexone as it can block pain relief medications
Signs of liver problems: yellowing of skin or eyes, dark urine, severe stomach pain
Severe depression or thoughts of self-harm
Severe allergic reaction: difficulty breathing, facial swelling
Injection site reactions with Vivitrol: severe pain, hardness, or tissue damage
Severe nausea or vomiting lasting more than a few days

Tips for getting started

If starting for opioid use disorder, confirm with your doctor that you have been completely opioid-free long enough — starting too early causes sudden, severe withdrawal. For alcohol use disorder, naltrexone does not require abstinence before starting. Consider the monthly injection (Vivitrol) if daily pill adherence is a challenge. Combine with counseling or support groups (AA, SMART Recovery) for the best outcomes. Carry a medical ID card noting naltrexone use for emergency situations.

Frequently asked questions

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References

[Regulatory] FDA Prescribing Information for ReVia (naltrexone) https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/018932s017lbl.pdf Accessed 2026-03-01.
[Regulatory] SAMHSA Treatment of Opioid Use Disorder https://www.samhsa.gov/medications-substance-use-disorders/medications-counseling-related-conditions/naltrexone Accessed 2026-03-01.
[Regulatory] NIAAA: Naltrexone for Alcohol Use Disorder https://www.niaaa.nih.gov/alcohols-effects-health/alcohol-use-disorder/treatment Accessed 2026-03-01.

Written and fact-checked by PrescriptionDrugs.org Editorial Team

Last updated: March 1, 2026