Naltrexone

Naltrexone blocks opioid receptors. Its FDA-approved job, per the label for the 50 mg tablet, is the treatment of alcohol dependence and the blockade of the effects of externally administered opioids. It is not a weight-loss drug on its own, and the label is explicit that it has not been shown to provide therapeutic benefit outside that context.

It appears in this glossary because of Contrave, where 8 mg of naltrexone is paired with 90 mg of bupropion. The rationale is a feedback loop: bupropion stimulates appetite-suppressing neurons in the hypothalamus, and those neurons release a signal that partly shuts themselves off through opioid receptors. Blocking that receptor removes the brake. Neither drug does much for weight alone; together they do more.

There is a third context readers encounter online: low-dose naltrexone, typically 1.5 to 4.5 mg, prescribed off-label for chronic pain, fibromyalgia and various inflammatory conditions. That use is not FDA-approved, the doses are a fraction of the labeled 50 mg, and the products are usually compounded. It is a genuinely different thing from either Contrave or alcohol-dependence treatment, and conflating the three is the most common source of confusion here.

The safety point that matters most: because naltrexone blocks opioid receptors, it is contraindicated with chronic opioid use or during acute opioid withdrawal. That includes prescription pain medication. Anyone who might need opioid analgesia — for surgery, an injury, a dental procedure — needs their care team to know they are taking it.

Worth asking your clinician: whether you take any opioid medication, even occasionally; whether alcohol use is part of what is driving your eating; and whether Contrave’s contraindication list applies to you. Our naltrexone and Contrave evidence review and GLP-1 plus naltrexone page go deeper, and the Contrave side-effect review covers tolerability.