Background: Data from California and Washington note decreases in heroin and synthetic opioid injection and increases in smoking (previously thought rare). The full US national extent of these changes is unknown.
Objectives: 1) examine US national and regional trends in injection vs non-injection (i.e., smoking and sniffing) routes of administration (ROA) of heroin and synthetic opioids; and, 2) identify associations with ROA preferences.
Methods: We analyzed 7,881,318 admissions for heroin or synthetic opioid treatment in the SAMHSA Treatment Encounter Data Set from 2000 to 2021. The primary outcome was ROA preference. We calculated annual ROA proportions nationally and by region. We performed regressions to identify associations with injection versus non-injection use and among non-injection ROAs.
Results: In 2021, injection ranged from 46-56%, down across all regions from earlier peaks. From 2000 to 2021, smoking increased sharply in many western states and grew modestly elsewhere. Regression analysis confirmed the strong association between region and smoking. Being indigenous, younger, unstably housed, and having fewer prior treatment admissions increased odds of smoking, while being Black or Latino decreased them.
Discussion: Smoking is now common across western states and growing in eastern states. It should reduce injection-specific morbidity (e.g., HIV, HCV, endocarditis, skin infections, and vein damage); however, there is an urgent need to understand the unique health risks associated with smoking heroin and its adulterants including fentanyl and xylazine. Clinicians, researchers, and harm reductionists should be alert to these shifting ROA preferences.