"Our population-based study provides evidence that police seizures of substances identified as opioids or stimulants are significantly associated with increased spatiotemporal clustering of overdose events in the immediate surrounding geographic area (radii of 100 m, 250 m, and 500 m) over 1-, 2-, and 3-week periods.

"Our findings contribute further evidence supporting tenant-led naloxone distribution and overdose education as a critical intervention to address overdose vulnerability in SRO [Single Room Occupancy] settings (Bardwell et al., 2019; Nowell & Masuda, 2020).

"In 2021, the SFDPH [San Francisco Department of Public Health]/DOPE [Drug Overdose Prevention & Education] Project collaboration initiated a pilot program designed to reduce fatal overdoses in permanent supportive SROs by mobilizing and supporting tenant overdose response within these buildings.

"Heroin Assisted Treatment (HAT) is an alternate treatment modality for people for whom more traditional forms of OST have been ineffective. HAT is currently delivered in seven countries worldwide (Switzerland, Canada, Germany, Holland, Denmark, Luxembourg and the UK) with the longest standing programme operating in Switzerland. The service usually comprises provision of synthetic medical grade heroin (diacetylmorphine) for supervised self-injection, under medical supervision in a clinical environment.

"Opioid substitution therapy (OST) is an evidence-based treatment for opioid dependency, with treatment engagement shown to be protective against drug related deaths (Santo et al., 2021). In England, the primary OST medications prescribed are methadone and buprenorphine, with provision ranging from daily supervised consumption at pharmacy services to take-home weekly doses.

"In 2020 drug related deaths in the United Kingdom (UK) reached the highest rate in over 25 years (ONS, 2021). Data between 2001-2018 evidences a substantial increase in drug poisonings over time for people who use opioids, with risk increasing particularly between the years of 2010-2018, an effect which was not entirely explained by the ageing of this cohort (Lewer et al., 2022).

"The high prevalence of mental health issues among the homeless population has been extensively documented throughout literature, but the consumption of NPS to treat mental health symptoms is of particular concern (Gray et al., 2021; Irving et al., 2015; McLeod et al., 2016; Ralphs et al.,

"The prevalence of homelessness globally is estimated to be roughly 150 million individuals at any given time (Busch-Geertsema et al., 2016). In the UK, recent data from the Shelter organisation estimated that 320,000 people were homeless in 2019/2020 (Bramley & Fitzpatrick, 2018).

"This research sought the perspectives of people involved in the unregulated drug market on how drug checking could be implemented as a market intervention within the current context of a highly unpredictable drug supply and unprecedented rates of overdose. Currently, drug checking is positioned as a public health intervention promoted to people who use drugs within supervised consumption sites while being averse to aiding people who sell or produce drugs.

"The adulteration of illicit drugs is not a new phenomenon, with evidence of it occurring as early as the 1930s (Morgan, 1982).