We report two 16-year-old female intravenous drug users who, after making purchases from street suppliers, both presented with symptoms of acute opioid withdrawal. Urine toxicology revealed naltrexone, a long-acting opioid antagonist used in detoxification and maintenance therapy in opioid dependence. While the safety and efficacy of opiate antagonist treatment is being debated, the present case highlights the vulnerability of this young population. The recent availability of non-prescribed opiate antagonists suggests that both health professionals and young people themselves need to be aware of their effects.