ANALYSIS: The rapid growth in the global use of new synthetic opioids (NSOs) including fentanyl and nitazenes prompted the UK’s National Crime Agency to warn last year that “there has never been a more dangerous time to take [illegal] drugs”; Dr Philip Berry, a Visiting Research Fellow at King’s College London and expert on the international drugs trade, looks at the background to the growth in NSOs, the nitazene ‘boom’ and the global heroin market, and what lessons the UK and Europe can learn from the US experience.