Croop 1997: naltrexone side effects in 570 people treated for alcohol

What they tested

This 12-week study ran in 40 alcohol treatment centers across the US, including treatment programs, university clinics, Veterans Administration hospitals and primary care practices. It was set up to collect safety data in conditions like the expected everyday use of the drug.

Doctors decided who got naltrexone and who went into a reference group with no study medicine, so people were not randomly assigned, and everyone knew what they were taking. All had been abstinent for 1 to 6 weeks and were in a counselling program. Women and people with other medical or psychiatric illnesses, often left out of trials, could join, and people using other drugs or with HIV were not excluded.

What they found

Of 865 people enrolled, 570 received naltrexone and 295 were in the reference group.

Nausea (9.8%) and headache (6.6%) were the most common new problems in the naltrexone group. Naltrexone was stopped in 15.0% of people because of side effects, most often nausea.

Liver function test results in the naltrexone group were similar to those in the reference group. No one died during the study, and the authors identified no new safety concerns.

Limits

• There was no placebo group and no random assignment. Doctors chose who got naltrexone, so the two groups may have differed in ways that affect side effects and liver tests.
• Everyone knew whether they were taking naltrexone, which can affect what side effects people report.
• It lasted 12 weeks, so it can't show rarer or later problems, and everyone had already stopped drinking for 1 to 6 weeks.

What it means if you're considering naltrexone

This is the largest early look at naltrexone's side effects in a mix of people like those seen in real clinics, and the site's side-effect guides lean on it. For most people, the side effects to expect are nausea and headache, and nausea was the main reason people stopped.

The liver results are reassuring, but this study wasn't designed to prove safety the way a placebo-controlled trial would, and the drug label has its own liver guidance.