Deaths from synthetic opioids, natural and semi-synthetic opioids, and heroin totalled 49 068 in 2017 in the USA, with the sharpest increase occurring in fatal overdose related to oxycodone, fentanyl, and fentanyl analogues. In Europe, five fentanyl derivatives were identified in 2017, and these are being mixed with other drugs, including heroin and cocaine. The danger of mixing different drugs is that the user is often unaware of which substances they are consuming with the result that they are at even greater risk of overdose—particularly problematic with fentanyl, which is estimated to be between 50 and 100 times more potent than heroin.