Drug-related deaths (DRD) are a significant and increasing public health problem in Scotland. Benzodiazepines and BZD-type substances (BZD) are increasingly implicated in DRD. In 2018, BZDs were implicated in 67% of DRD, often in combination with other illicit and prescribable substances including Opiate Replacement Therapies (ORT) such as methadone and buprenorphine.

Illicit BZD use and dependence is higher among people with other substance use disorders. 29% of patients presenting to Scottish addiction services report current illicit BZD use. There is widespread variance in approaches to the clinical management of BZD dependence among people with opioid use disorder in Scotland. Some addiction clinicians are reluctant to prescribe BZD to people on ORT, some will prescribe BZD with the primary aim of dose reduction and detoxification, others will consider longer-term maintenance prescribing whilst patients stabilise on ORT.

Previous research has identified increased risks of mortality among people taking BZD and ORT. Other work suggests that co-prescribing BZD and ORT increases patient engagement and retention in addiction treatment.

This retrospective cohort study will analyse anonymised, linked data on people who received ORT between 01/01/2010 and 31/12/2020 to explore any relationships between exposure (co-prescribing of BZD and ORT) and harms including: mortality (all-cause and DRD), hospitalisation, illicit drug use during ORT, and reduced retention in addiction care.

Scotland is experiencing a 'public health emergency' of escalating drug-related deaths (DRD) in which benzodiazepine (BZD) are increasingly implicated, often in combination with other substances (National Records of Scotland, 2019; Scottish Government, 2019).

In 2008 BZD were implicated in 26% (n=149) of DRD and were exclusively prescribable drugs such as diazepam, although the source is not known. By 2018 BZD and BZD-type drugs were implicated in 67% (792) of DRD, predominately substances not available on prescription in the United Kingdom (UK) such as etizolam and alprazolam (Xanax). We refer to these as illicit BZD.

People who use illicit BZD, of unknown constituents and potency, can inadvertently or deliberately consume megadoses of BZD many times in excess of safe therapeutic doses, often with alcohol and other drugs, which combine to increase the risk of harm and death. Rights, Respect and Recovery, the current drug and alcohol strategy, expressed Scottish Government concern regarding the increased prevalence and potency of BZD-type drugs.

People presenting to addiction services for initial assessment frequently report illicit BZD use in the month prior to assessment, an average of 2,561 (29%) per year in the past five years for which data are available. The prevalence of illicit BZD use is known to be higher among people with other substance use disorders, especially problematic opiate and/or alcohol dependence. A systematic review identified a high prevalence (typically >40%) among people on Opiate Replacement Therapy (ORT).

The picture of BZD prescribing among people on ORT is complex and evolving. Previous work shows that BZD prescribing among ORT patients is associated with increased harms including mortality, but conversely protective factors such as increased engagement in care. Scottish addiction specialists have confirmed that some addiction services are exploring maintenance prescribing to reduce the risks associated with illicit BZD use among ORT patients. However clinical guidance does not currently provide a framework for this. Evidence of patient safety and other outcomes from BZD prescribing in the context of ORT is sparse and conflicting. A 2018 Cochrane review concluded "it is not possible to draw firm conclusions regarding pharmacological interventions to facilitate BZD discontinuation in chronic BZD users". Recent UK public health alerts have highlighted the need for caution and additional monitoring when co-prescribing BZD and ORT, and the need for improved harm reduction advice regarding the risk of illicit BZD. Addiction clinicians have indicated there has been disagreement among certifying pathologists regarding the role of benzodiazepines in DRD.

There is a need to understand patterns of, and outcomes from, BZD prescribing among ORT patients in Scotland to inform safe and effective clinical practice, address problematic BZD use in the content of poly-drug use, and reduce the risk of harms including mortality among people who use drugs (PWUD).

The cohort will consist of people who were prescribed ORT between 01/01/2010 and 31/12/2020. The definition of ORT is based on the following medications and associated British National Formulary (BNF) codes:

Chemical (BNF code): Buprenorphine Hydrochloride/Naloxone Hydrochloride (0410030B0); Buprenorphine Hydrochloride (0410030A0); Methadone Hydrochloride (0410030C0)

The study population includes people who received medication assisted treatment for the management of opiate / opioid addiction from community settings (e.g. community-based specialist addiction services and primary care physicians 'General Practitioners').