| Outer setting |
| [Contextual factors that influence successful implementation] | Patient needs and resources | Stigma, trauma and criminalization; unpredictable illicit market; diverse population and needs |
| External policy and incentives | Criminalization of drugs and people who use drugs |
| Intervention characteristics |
| [Key attributes of drug checking a harm reduction intervention that influence successful implementation] | Relative advantage | Low barrier and greater benefits than risks of criminalization |
| Evidence strength and quality | Accuracy of drug checks providing information on composition using a small sample |
| Design quality and packaging | Free and fast service |
| Adaptability | Harm reduction messaging |
| Inner setting |
| [Key attributes of drug checking services and sites that influence successful implementation] | Culture and compatibility | Safety; respect; confidential and anonymous service; and harm reduction mandate |
| Available resources | Multiple settings to meet diverse needs; paired with compatible services; pharmacies; mobile services |
| Characteristics of individuals |
| [Key attributes of drug checking staff that influence successful implementation] | Knowledge and beliefs | Skilled technicians and trust, respect and freedom from judgement |
| Process of implementation |
| [Key attributes related to the process of implementing drug checking services that influence successful implementation] | Engaging and external change agents | Engaging people with lived and living experience in implementation and the intervention |
