Table 1 Summary of included studies (n = 50), grey literature (n = 5) and how they contributed to the final theories

Ambrose et al., 2016¹

Bivariate and multivariate associations, sensitivity analysis

Harm reduction programme

X

X

Baca et al., 2007²

Qualitative structured interviews

Harm reduction programme, syringe exchange (low threshold)

X

Banjo et al., 2014³

Evaluation (mixed methods)

BCCD harm reduction programme

X

X

X

X

X

Behar et al., 2015⁴

Survey (repeated measures)

DOPE programme (low threshold), syringe exchange (low threshold)

X

X

Bennett et al., 2011⁵

Evaluation (survey, repeated measures)

Harm reduction programme

Negative attitudes (police)

X

X

X

X

Bennett& Holloway, 2012⁶

Evaluation (survey, repeated measures)

Harm reduction programme

X

Beswick et al., 2002⁷

Qualitative structured interviews

Unknown

X

Bowles et al., 2019⁸

Qualitative semi structured interviews

Harm reduction programme, syringe exchange (low threshold)

X

X

Clark & Eustace, 2016⁹

Evaluation (mixed methods-repeated measures and semi-structured interviews)

Harm reduction programme

Negative attitudes (General Practitioner [GP])

X

Chronister et al., 2018¹⁰

Evaluation (survey repeated measures)

Harm reduction, low threshold health care facility and abstinence-based programmes where low threshold services are embedded

X

X

X

Das et al., 2017¹¹

Case study

Needle exchange (low threshold)

X

Dettmer et al., 2001¹²

Case study

Health care project, mobile drug services (low threshold)

X

X

Doe-Simkins et al., 2009¹³

Evaluation (prospective cohort)

Needle exchange (low threshold)

X

X

X

X

Doe- Simkins et al., 2014¹⁴

Retrospective cohort study

Syringe exchange (low threshold)

X

X

X

X

Dwyer et al., 2015¹⁵

Evaluation (survey repeated measures)

Low threshold, detoxification centres, abstinence-based residential drug treatment

X

X

X

Enteen et al., 2010¹⁶

Evaluation (prospective cohort)

DOPE programme (low threshold), syringe exchange (low threshold) opioid substitution clinic, hostels

X

X

X

Espelt et al., 2017¹⁷

Survey (repeated measures)

Needle exchange (low threshold), outreach, supervised injection facilities (harm reduction)

X

X

EuroNPUD, 2019¹⁸

Report (grey literature)

 Unknown

X

X

X

Galea et al., 2006¹⁹

Pilot (pre-/post-overdose experiences)

Syringe exchange (low threshold)

X

X

Gaston et al., 2009²⁰

Evaluation (prospective cohort, survey repeated measures)

Abstinent-based programme (inpatient and outpatient)

Negative attitudes (police)

X

George et al., 2010²¹

Case study

Community drug team

X

X

Gilbert et al., 2018²²

Randomised controlled trial

SKOOP training programme (harm reduction)

X

X

Green et al., 2008²³

Between groups (trained vs untrained, questionnaire)

Needle exchange (low threshold) and abstinence-based drug treatment centre

X

Green et al., 2014²⁴

Case study

Prison naloxone programme

X

X

X

Farrugia et al., 2019²⁵

Case study

Peer run drug consumer organisation

X

X

Khatiwoda et al., 2018²⁶

Mixed methods (survey and open-ended questions)

Harm reduction

X

X

Lankenau et al., 2013²⁷

Evaluation qualitative-closed and open-ended questions)

Syringe exchange (low threshold), community health care programmes

Negative attitudes (police)

X

X

X

X

X

Leece et al., 2013²⁸

Evaluation (cohort)

Syringe exchange (low threshold)

X

X

Leece et al., 2016²⁹

Evaluation (mixed methods-survey and one-to-one interviews)

Syringe exchange (low threshold)

X

X

X

Madah-Amiri, et al., 2017³⁰

Evaluation (prospective cohort, overdose prevention behaviours)

Syringe exchange, supervised injection site (low threshold)

X

X

X

Maldah-Amiri, et al., 2019³¹

Prospective cohort (survey, repeated measures)

Syringe exchange (low threshold)

X

X

Maldjian, et al., 2016³²

Prospective cohort (survey, repeated measures)

Syringe exchange (low threshold)

X

X

Maxwell (2006)³³

Report (prospective cohort, post training knowledge)

Chicago Recovery Alliance programme (harm reduction)

X

McAuley et al., 2010³⁴

Evaluation (prospective cohort, post training knowledge)

Lanarkshire naloxone project (low threshold)

X

Nelson et al., 2016³⁵

Evaluation (mixed methods, survey repeated measures, one-to-one interviews)

Low threshold

X

X

X

X

NIHD (n.d.)³⁶

Report (post training actions taken in an overdose)

Harm reduction

X

X

Olsen et al., 2015³⁷

Evaluation (mixed methods-survey repeated measures, semi-structured interviews)

Harm reduction

X

X

X

PHA, 2016³⁸

Report (post training)

Low threshold services

X

X

X

Parmar et al., 2017³⁹

Randomised control pilot trial

N-Alive programme (low threshold)

X

Piper et al., 2008⁴⁰

Evaluation (survey)

SKOOP programme (harm reduction)

X

Rowe et al., 2015⁴¹

Survey

Harm reduction

X

X

Ruane, 2019⁴²

News article (describing barriers to naloxone programmes)

Harm reduction

Negative attitudes (GP)

X

Seal et al., 2005⁴³

Pilot study (prospective cohort, survey)

Harm reduction

Negative attitudes (Police)

X

X

X

X

Sherman et al., 2008⁴⁴

Qualitative one-to-one semi-structured interviews

Harm reduction centre, syringe exchange (low threshold)

Negative attitudes (ambulatory staff)

X

X

X

Sherman et al., 2009⁴⁵

Qualitative one-to-one interviews

Staying Alive programme (low threshold), needle exchange (low threshold)

X

X

X

Shorter & Bingham, 2016⁴⁶

Evaluation (qualitative semi structured interviews)

Negative attitudes (police)

X

Siegler et al., 2017⁴⁷

Prospective cohort (questionnaire)

Syringe exchange programme (low threshold)

X

X

Strang et al., 2008⁴⁸

Prospect cohort (pre-/post-training questionnaire)

Abstinence-based inpatient and outpatient drug treatment programme

X

Tobin et al., 2009⁴⁹

Evaluation (prospective cohort, pre-/post-training)

Staying Alive programme (harm reduction), syringe exchange (low threshold)

X

X

X

Traynor, 2019⁵⁰

News article (reports of actions taken in an overdose)

Harm reduction and community outreach programmes

X

X

Wagner et al., 2010⁵¹

Evaluation (questionnaire)

Harm reduction

X

X

X

Wagner et al., 2014⁵²

Qualitative one-to-one interviews

Syringe exchange within a community health care, Homeless Health Care, Los Angeles centre for harm Reduction, Skid Row

Negative attitudes (police)

X

X

X

Walley et al., 2013⁵³

Interrupted time series analysis

Harm reduction, Chicago Recovery Alliance programme

X

X

Worthington et al., 2006⁵⁴

Qualitative focus group interviews

Lower east side harm reduction centre

Negative attitudes (police)

X

X

Yokell et al., 2011⁵⁵

Evaluation (post training)

Mixed: syringe exchange, AIDS outreach, homeless shelters, abstinence-based substance abuse treatment programmes

X