In this article by Eugene A. Kiyatkin, "Respiratory Depression and Brain Hypoxia Induced by Opioid Drugs: Morphine, Oxycodone, Heroin, and Fentanyl," published in NIH National Library of Medicine, the damage incurred as a result of overdosing makes you wonder why this is not more widely known. 

Kiyatkin EA. Respiratory depression and brain hypoxia induced by opioid drugs: Morphine, oxycodone, heroin, and fentanyl. Neuropharmacology. 2019 Jun;151:219-226. doi: 10.1016/j.neuropharm.2019.02.008. Epub 2019 Feb 5. PMID: 30735692; PMCID: PMC6500744.