Larney 2014: what the evidence says about naltrexone implants

What they tested

The authors looked for studies that compared naltrexone implants, pellets placed under the skin that release the drug over time, with another treatment or a placebo. They looked at starting treatment, staying in treatment, opioid and other drug use, side effects, non-fatal overdoses and deaths.

Randomized trials were pooled in a meta-analysis. Non-randomized studies were described in words rather than pooled. The quality of the evidence was graded with GRADE, a standard system for rating how much a body of evidence can be trusted.

What they found

Implants did better than placebo implants (risk ratio 0.57) and naltrexone pills (risk ratio 0.57) at suppressing opioid use. Each of those results came from just 2 trials.

One study compared implants with methadone maintenance and found no difference in opioid use, but the authors rated that evidence low quality.

Overall, they judged the evidence on implant safety and effectiveness limited in amount and quality, and of little use in places where effective opioid treatments are already available. They concluded that implants should be limited to clinical trials until better-designed research is done.

Limits

• The main pooled results each rested on only 2 trials.
• Evidence quality ranged from moderate to very low.
• The abstract doesn't give pooled results on side effects, overdose or death, even though the review looked at them.

What it means if you're considering naltrexone

For someone considering a naltrexone implant for opioid use, this review is a caution: the trials that exist look favorable, but there are few of them and their quality is mixed. The site's implant guide notes that no implant is FDA-approved in the US, and that the approved long-acting form is the monthly Vivitrol shot.