The global war on drugs has been fought for 50 years, without preventing the long-term trend of increasing drug production, supply and use. But beyond this failure to achieve its own stated aims, the drug war has also produced a range of serious, negative costs. Many of these costs have been identified by the United Nations Office on Drugs and Crime (UNODC) – the very UN agency that oversees the system responsible for them – and are described as the ‘unintended consequences’ of the war on drugs. They may have been unintended, but after more than 50 years, they can no longer be seen as unanticipated. These costs are distinct from those relating to drug use, stemming as they do from the choice of a punitive, enforcement-led approach, the burden of which – as with all wars – tends to fall most heavily on the most vulnerable in society, including children and young people. This briefing summarises these costs.