Social affairs correspondent Robert Booth tells Madeleine Finlay why a class of synthetic opioids called nitazenes, first developed in the 1950s, is leading to a worrying number of fatal overdoses in the UK. And she hears from toxicology and addiction specialist Dr Joseph D’Orazio about a tranquilliser called xylazine that has been showing up in alarming volumes in the US illegal drug supply and is now starting to appear in toxicology reports in the UK. Help support our independent journalism at theguardian.com/sciencepod