The most important things to avoid when taking naltrexone are opioid medications, large doses of alcohol (if you’re not using naltrexone specifically for alcohol reduction), and anything that puts extra strain on your liver. Naltrexone works by blocking opioid receptors in the brain, which means it directly interferes with certain drugs and changes how your body responds to alcohol. Knowing what to steer clear of helps you stay safe and get the most out of treatment.
Opioid Medications and Street Drugs
This is the single biggest thing to avoid. Naltrexone blocks the same receptors that opioids attach to, so taking any opioid while on naltrexone creates two serious risks.
First, opioid painkillers simply won’t work. If you take a normal dose of codeine, hydrocodone, oxycodone, morphine, or any other opioid, naltrexone will block the pain relief entirely. This matters if you need emergency surgery or dental work. You should carry a card or wear a medical alert bracelet letting providers know you take naltrexone, because standard opioid pain management won’t help you.
Second, and more dangerous: some people try to “override” the blockade by taking very large amounts of opioids. This can cause a fatal overdose. Naltrexone’s blocking effect eventually wears off, and if there’s a massive amount of opioid in your system at that point, respiratory failure can happen quickly. Even while naltrexone is active, extremely high opioid doses can partially overcome the blockade and cause unpredictable, life-threatening effects.
Street drugs like heroin and illicitly manufactured fentanyl fall into this same category. If you’re taking naltrexone for opioid use disorder and you relapse, your tolerance will be significantly lower than it was before treatment. That reduced tolerance makes overdose far more likely, especially once naltrexone clears your system.
Opioid-Containing Cough and Diarrhea Products
Some over-the-counter and prescription products contain opioids that people don’t always recognize. Cough syrups with codeine, certain prescription antidiarrheal medications, and combination cold products can all contain opioid ingredients. These won’t provide their intended effect while you’re on naltrexone, and they can trigger withdrawal symptoms if you have any opioids still in your system. Check ingredient labels or ask a pharmacist before taking cold, flu, or stomach remedies.
Alcohol: What Actually Happens
The relationship between naltrexone and alcohol is more nuanced than with opioids, because naltrexone is actually prescribed to help people drink less. It doesn’t make you sick if you drink the way disulfiram (Antabuse) does. There’s no vomiting reaction or dangerous blood pressure spike from combining the two.
What naltrexone does is block the pleasurable “buzz” that alcohol normally produces. It binds to endorphin receptors and prevents alcohol from triggering the reward response in your brain. Over time, this reduces cravings and the total amount you drink. Some treatment programs, like the Sinclair Method, specifically instruct people to take naltrexone before drinking.
That said, naltrexone doesn’t block all of alcohol’s effects. You can still become impaired, your coordination and judgment will still suffer, and alcohol still damages your liver. If you’re taking naltrexone for opioid recovery rather than alcohol reduction, heavy drinking adds unnecessary liver stress on top of the medication. The combination deserves a straightforward conversation with your prescriber about your drinking habits.
Anything That Stresses Your Liver
Naltrexone carries an FDA boxed warning about the potential for liver damage. At the standard 50 mg daily dose used for alcohol or opioid treatment, clinically significant liver injury is uncommon. But the risk increases if your liver is already compromised.
This means you should be cautious with other substances that tax the liver. High doses of acetaminophen (Tylenol) are a common culprit, especially when combined with alcohol. Certain herbal supplements, particularly kava and comfrey, are known to strain liver function. Anabolic steroids and some prescription medications processed through the liver can also compound the risk.
Your prescriber will typically check liver enzyme levels before starting naltrexone and may monitor them periodically. If you have existing liver disease, hepatitis, or significantly elevated liver enzymes, naltrexone may not be appropriate for you. People with severe liver impairment have not been adequately studied in clinical trials, so the safety profile in that group remains unclear.
Starting Too Soon After Opioid Use
If you’ve recently used opioids, starting naltrexone too early will throw you into sudden, intense withdrawal. This happens because naltrexone rips opioids off receptors that are already occupied, triggering symptoms within minutes rather than the gradual onset of normal withdrawal.
Precipitated withdrawal is significantly more severe than typical withdrawal. It can include extreme nausea, vomiting, diarrhea, muscle cramps, anxiety, and agitation, all hitting at once. For short-acting opioids like heroin, most protocols require at least 7 to 10 days of abstinence before starting naltrexone. For long-acting opioids like methadone, the waiting period is often 10 to 14 days or longer. A naloxone challenge test is sometimes used to confirm that opioids have sufficiently cleared your system before the first naltrexone dose.
Kidney Considerations
Naltrexone and its primary breakdown product leave the body through the kidneys. If you have impaired kidney function, the drug can accumulate to higher-than-expected levels. The FDA label recommends caution in people with renal impairment, though specific dose adjustment guidelines haven’t been established through formal studies. If you know your kidney function is reduced, make sure your prescriber is aware so they can weigh the risks and monitor appropriately.
Pregnancy and Breastfeeding
The safety data on naltrexone during pregnancy is limited. Animal studies have shown some developmental effects at high doses, but well-controlled human studies are lacking. For pregnant women with opioid use disorder, other medications with more established safety profiles are generally preferred. Naltrexone’s opioid-blocking properties also raise practical concerns: if you go into labor and need opioid pain relief, it won’t be effective.
Whether naltrexone passes into breast milk in meaningful amounts is not fully established. If you’re pregnant, planning to become pregnant, or breastfeeding, the decision to use naltrexone requires weighing the benefits of treatment against the unknowns.
Supplements and Herbal Products
Some supplements interact with naltrexone in ways that aren’t always obvious. Kratom, which acts on opioid receptors, will be blocked by naltrexone and could trigger withdrawal-like symptoms in people who use it regularly. Poppy seed products, while unlikely to cause problems in small culinary amounts, can contain variable levels of opioid compounds.
St. John’s wort and other supplements that affect liver enzymes could theoretically alter how quickly your body processes naltrexone, though formal interaction studies are sparse. The safest approach is to tell your prescriber about everything you take, including supplements, so they can flag potential issues.