Patterns, circumstances and risk factors associated with non-fatal substance overdose in a cohort of homeless population: an observational study.

Background: Non-fatal overdoses frequently precede fatal overdoses, thus identifying risk factors for non-fatal overdoses could help develop strategies to prevent substance related deaths.

Aim: This study aimed to identify patterns, circumstances and risk factors leading to non-fatal substance overdose in people experiencing homelessness.

Method: All recorded cases of non-fatal substance overdose from a population of people experiencing homelessness registered at a specialist homelessness primary care centre in England were identified using electronic medical records. Overdose details and patient characteristics were extracted. The heterogeneity between variables in people with and without a recorded non-fatal overdose were tested and multivariable logistic regressions were used to identify the risk factors of non-fatal overdoses.

Results: From the 1221 registered patients, 194(16%) were identified as having had a non-fatal overdose with 428 overdoses between them. Half were polypharmacy events with the main substances of overdose being: heroin, paracetamol, benzodiazepines, cocaine, antipsychotics, SSRIs and synthetic cannabinoids. Risk of non-fatal overdose was greater in females, white ethnicity, ages 36-45, and in those with a recorded use of tobacco, alcohol or illicit substance use. Chronic physical and mental health conditions increased the risk of non-fatal overdose including respiratory conditions, blood borne viruses, migraines, anxiety and depression.

Conclusion: With a high number of non-fatal overdoses within this population, identifying individuals at risk based on the factors identified in this research could enable primary care providers to apply prevention actions such as overdose awareness and naloxone provision to avoid drug harm and deaths. Future work should explore the role of chronic physical conditions and their treatment on non-fatal overdose risks.