The opioid antagonist naltrexone does not appear to increase the risk of serious adverse events over placebo, researchers from the University of Manchester have found
The researchers carried out a systematic review and meta-analysis of 89 randomised controlled trials involving over 11,000 participants. Each of the trials were carried out for at least four weeks and examined the risk of adverse events with oral naltrexone compared with placebo.
Most trials considered the risks of naltrexone in its licensed indications, (i.e. alcohol use disorders and other addictions), but there were also studies on psychiatric disorders, impulse control disorders, Crohn’s disease and cancer. People taking opioids were excluded.
The results showed no significant difference in the rate of serious adverse events between naltrexone and placebo. Secondary analysis revealed only six marginally significant adverse events for naltrexone when compared with placebo, but these were of mild severity.
The researchers said that naltrexone is increasingly being used for off-label indications and may be taken by patients for long periods of time, so it was important to have clarity over its safety.
“These findings confirm the safety of oral naltrexone when used in licensed indications and encourage investments to undertake efficacy studies in unlicensed indications,” they concluded in BMC Medicine (15 January 2019).
 Bolton M, Hodkinson A, Boda S et al. Serious adverse events reported in placebo randomised controlled trials of oral naltrexone: a systematic review and meta-analysis. BMC Medicine 2019;17:10. doi: 10.1186/s12916-018-1242-0