Mr G, 80, using a fentanyl patch for chronic back pain, developed a fever from a chest infection and, over the same day, became drowsy, pinpoint-pupilled and confused, with a slowing respiratory rate. The infection was real, but the delirium was opioid toxicity. Fever and warm skin had increased the absorption from his patch, and a dose that had been stable for months was suddenly delivering far more. The heat had turned a steady drug into an overdose. We removed the patch, but the point the team almost missed is that removal alone is not enough. The drug already absorbed sits in a depot under the skin and keeps releasing for many hours, so he needed close monitoring for a full day, with naloxone to hand and given in small titrated doses if his breathing worsened. Transdermal opioids deliver more when the patient is hot, whether from fever, a heatwave or a hot pack. In any febrile patient on a fentanyl patch who becomes drowsy and confused, think opioid toxicity, remove the patch, and keep watching well beyond it. #delirium