Garbutt 2005: the monthly naltrexone shot trial behind Vivitrol

What they tested

Adults with alcohol dependence who were actively drinking were randomly given a monthly injection into the muscle of 380 mg long-acting naltrexone (205 people), 190 mg (210 people) or a matching placebo (209 people). Neither they nor the staff knew which. Everyone also had 12 sessions of a low-intensity counselling program.

The main outcome was the event rate of heavy drinking days, a measure of how often heavy drinking days happened over the 6 months, counting everyone randomized.

What they found

Compared with placebo, the 380 mg dose led to a 25% decrease in the event rate of heavy drinking days (P = .02). The 190 mg dose led to a 17% decrease (P = .07), which was not statistically significant.

The benefit differed by group. Men, and people who had stopped drinking before the first injection, showed greater treatment effects.

Stopping because of side effects happened in 14.1% on 380 mg, 6.7% on 190 mg and 6.7% on placebo. Overall, the rate and timing of people leaving treatment were similar across groups.

Limits

• The clearer benefit was in men and in people who had already stopped drinking before the first shot, so women and people still drinking at the start may get less from it.
• It lasted 6 months, so it can't say what happens with longer use or after stopping.
• More people stopped because of side effects on the 380 mg dose (14.1%) than on placebo (6.7%).

What it means if you're considering naltrexone

This is the main trial behind Vivitrol, the monthly naltrexone shot, approved for alcohol dependence in 2006. It showed a shot once a month can lower heavy drinking without daily pills, which matters for people who struggle to take tablets every day.

The benefit was larger in men and in people who had stopped drinking before starting, and side effects led more people to stop on the 380 mg dose.