1. National Institue on Drug Abuse (NIDA) Overdose deaths rates https://www.drugabuse.gov/related-topics/trends-statistics/overdose-death-rates http://www.webcitation.org/6sbmgABPX
2. Office for National Statistics Deaths Related to Drug Poisoning in England and Wales: 2015 registrations https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/deaths/bulletins/deathsrelatedtodrugpoisoninginenglandandwales/2015registrations http://www.webcitation.org/6sbn6mNUI .
3. EMCDDA European Drug Report 2017 http://www.emcdda.europa.eu/publications/edr/trends-developments/2017 http://www.webcitation.org/6uRuSPTES
4. Mortality among young injection drug users in San Francisco: a 10-year follow-up of the UFO study;Evans;Am J Epidemiol,2012