Naltrexone is a first-line treatment for alcohol use disorders in North America and Europe. It was prescribed to a 63-year-old patient in order to help control amounts of alcohol consumed per drinking occasion. The patient experienced a paradoxical, but consistent side effect of feeling inebriated each time he took naltrexone. In order to investigate this phenomenon we administered naltrexone and a placebo in a randomised double-blind fashion. The patient exhibited a 'high-like' response to all placebo capsules and a decrease in the subjectively perceived euphoria shortly after ingestion of naltrexone. Given that this placebo effect could be mediated via opioid receptors we suggest that this case illustrates the ability of naltrexone to eliminate the placebo effect. This feature of naltrexone, upon further investigation, might be used in randomised clinical trials in addition to or as an alternative to a placebo.