Opiate detoxification procedures aim to reduce intensity and duration of withdrawal. Ultra-rapid opiate detoxification (UROD) methods attempt to obtain this goal by administering naltrexone under deep sedation or anaesthesia. We present a case study on accidental ingestion of naltrexone in a methadone maintenance patient, which shows close methodological similarities with UROD procedures. Naltrexone was effective in reducing withdrawal duration, but not as much as UROD studies report. The administration of naloxone after detoxification did not trigger withdrawal symptoms, even in the presence of methadone, as detected by urinalyses. These results suggest the importance of further developing detoxification methods based on protocols of administration of antagonists different from UROD, in absence of anaesthesia.