Mitchell 1987: high-dose naltrexone for weight in men

What they tested

Men with obesity who were in dietary counselling first took a placebo, a dummy pill, for 2 weeks without knowing it. They then took either naltrexone 300 mg a day or a placebo for 8 weeks, with neither they nor the researchers knowing which.

The trial was based on animal research showing that blocking the body's own opioids reduces how much animals eat.

What they found

The results failed to show any advantage for naltrexone over placebo for weight loss.

Naltrexone was associated with hepatotoxicity, meaning liver injury, at this dose in these men.

Limits

• The abstract doesn't say how many men took part.
• Only men were included.
• The 300 mg dose is far higher than the tablet dose used for alcohol, so the liver finding speaks to high doses.

What it means if you're considering naltrexone

In this trial, a dose far above the one used for alcohol brought no weight benefit and signs of liver injury. It tested naltrexone alone, not Contrave, the naltrexone-bupropion tablet approved for weight management, so it says nothing about how that combination works.