The changing landscape of opioid use; strength, adultera-tion and implications for harm reduction

Background and aims: Heroin in the UK exhibits significant variability in potency and can be adulterated with other substances, posing substantial risks to users. Recently, the most concerning adulterants have been synthetic opioids such as nitazenes, which have potencies similar to fentanyl. Increasing deaths are associated with nitazenes, but at present there is no data on nitazene concentration in samples in the UK. Our study examines the current range of street heroin strength (3,6-diactylmorphine and 6-monoacetylmorphine), along with nitazene concentration in heroin and other samples. Additionally, we use our previously developed portable technology for drug discrimination, based on hybridized fluorescence/reflectance spectroscopy, to establish rapid identification of heroin strength from a small (2 mg) sample. Design, setting and participants: We sampled 80 suspected heroin/opioids which were conveyed to our laboratories via 5 regional police forces. Samples were selected based on risk perception or for contribution to police intelligence and public health. A sub-set of these samples originated as self-submissions to local charities. Measurements: Qualitative gas chromatography–mass spectrometry (GC-MS) and liquid chromatography–mass spectrometry were used to identify opioids and other relevant constituents, with concentration measured by quantitative nuclear mag-netic resonance spectroscopy and GC-MS. Findings: The submitted samples showed a very broad range of heroin (3,6–diacetylmorphine) strengths, with a bi-modal distribution centered at 19.4 ± 0.34% and 53.1 ± 0.7%. Self-submissions from people who use drugs were typically at the extremes of strength distribution, whereas police identified submissions showed more variance. Our portable technology can accurately identify heroin strength from a 2 mg sample presumptively as 0-20%, 20-40% and 40%+. Of the samples bought as heroin in powder form and found to contain nitazenes, the average nitazene concentration was 13.8 ± 2.5%; ~12-17 mg of nitazene in a heroin dose. 6-monoacetylmorphine had a concentration range of 0.5 – 16.5% in the heroin samples measured. It is typical for tablets to contain a large proportion of excipients and tablets containing nitazenes adhered to this trend with 1.1 ± 1.0%; 0.1-4 mg in a tablet. None of the tablets were sold as heroin, indeed some were presented to drug checking services as non-opioid sedatives. Conclusions: Users are exposed to an extremely broad variance in street heroin concentration from both 3,6-diactylmorphine and 6-monoacetylmorphine concentrations and this underscores the importance of quantifying samples to provide effective harm reduction advice. We demonstrate a technology solution to achieving this that could be implemented as part of a public health alerts/ early warning system or a drug checking service delivering rapid point of care results. The first reported quantification of nitazenes in UK heroin, tablet and powder samples, underscore the evolving landscape of opioid adulteration and the potential for heightened overdose risk.