Naltrexone is not habit-forming. It produces no euphoria, no high, and no reinforcing effects that would drive someone to misuse it. The U.S. Drug Enforcement Administration does not classify naltrexone as a controlled substance, and it is explicitly excluded from the schedules that cover addictive opioid-related drugs. This makes it fundamentally different from other medications used to treat addiction, like methadone or buprenorphine, which do carry some risk of dependence.
Why Naltrexone Cannot Produce a High
Naltrexone is an opioid antagonist, meaning it blocks opioid receptors rather than activating them. It binds tightly to the mu-opioid receptor, the same receptor that drugs like heroin and morphine stimulate to produce euphoria. But instead of switching that receptor “on,” naltrexone locks into place and prevents anything else from activating it. This is the opposite of what addictive opioids do. There is no reward signal, no rush, and no pleasurable sensation from taking it.
This blocking action is also why naltrexone works as a treatment for both opioid and alcohol use disorders. When someone drinks alcohol, the brain releases natural opioid-like chemicals (endorphins) that trigger dopamine release in the brain’s reward center. Naltrexone interrupts that chain. It reduces the rewarding feeling of drinking and dampens cravings triggered by environmental cues, like being in a bar or seeing alcohol advertisements. The result is that alcohol simply becomes less appealing over time.
No Evidence of Tolerance or Dependence
One hallmark of habit-forming drugs is that you need increasing doses to get the same effect. Research on naltrexone shows the opposite pattern. In animal studies spanning 30 and 60 days of repeated administration, naltrexone maintained its ability to suppress alcohol consumption without any sign of tolerance. The longer it was used, the more effectively it worked. Animals given naltrexone for 60 days showed greater suppression of alcohol intake than those treated for only 30 days.
Low-dose naltrexone (LDN), used off-label for chronic pain and inflammatory conditions at doses far below the standard 50 mg, shows the same safety profile. Researchers studying LDN for chronic pain have reported no cases of misuse, abuse, or dependence. When people stop taking LDN, their symptoms gradually return to baseline levels rather than producing withdrawal or rebound effects.
What Happens When You Stop Taking It
Stopping naltrexone does not cause the kind of physical withdrawal you would experience from quitting an addictive substance. There is no compulsion to keep taking it, and no dangerous rebound. However, people being treated for opioid addiction sometimes experience uncomfortable symptoms during naltrexone treatment that can be mistaken for a problem with the drug itself. These symptoms, sometimes called the “naltrexone flu,” include difficulty sleeping, muscle pain, sweating, chills, and runny nose.
These symptoms are more accurately understood as protracted withdrawal from the opioids the person was previously using, not as signs of naltrexone dependence. In a study of people on oral naltrexone for opioid use disorder, those who dropped out of treatment early reported an average of about 5 physical symptoms in their last week, compared to fewer than 1 symptom among people who completed treatment. The most commonly reported issues were difficulty sleeping (54% of early dropouts), runny nose (40%), and muscle pain (37%). These numbers reflect lingering opioid withdrawal, which naltrexone does not cause but also does not fully relieve.
How It Compares to Other Addiction Medications
This is where naltrexone stands apart most clearly. Methadone and buprenorphine, the two most common medications for opioid addiction, are partial or full opioid agonists. They activate the same receptors that heroin does, just more gently and in a controlled way. This approach is effective, reducing overdose deaths and illicit drug use, but it does maintain physical dependence. Patients who stop methadone or buprenorphine abruptly will experience withdrawal, and both medications carry some potential for misuse.
Naltrexone carries none of that risk. Because it blocks receptors instead of activating them, there is no physical dependence and no abuse potential. This is its most significant advantage over replacement therapies, though it comes with a tradeoff: patients have to be fully detoxed from opioids before starting naltrexone, and staying motivated to take a pill that offers no immediate reward can be challenging.
Side Effects Worth Knowing About
While naltrexone is not addictive, it is not side-effect free. Because it blocks the brain’s natural opioid system, which plays a role in everyday pleasure and social bonding, some people notice a blunted emotional range. Research on healthy adults has found that naltrexone reduces feelings of social warmth and the “liking” response to positive experiences. It can also decrease arousal in response to emotional situations. For most people these effects are subtle, but some experience noticeable anhedonia, a flattened ability to feel pleasure, which can contribute to discontinuation.
Naltrexone is also processed by the liver, so liver enzymes should be checked within a few weeks of starting treatment and every six months after that. People with existing liver problems may need closer monitoring or adjusted dosing. Common physical side effects include nausea, headache, and fatigue, which tend to be mild and often improve within the first few weeks of treatment.