Health risks associated with smoking versus injecting fentanyl among people who use drugs in California

Background: Given the attention, funding, and services that seek to reduce overdose mortality from fentanyl, it is important to understand whether a potential solution is for more people to switch from injecting to smoking fentanyl. As such, we set out to conduct a study to compare health and healthcare utilization outcomes associated with different modes of illicit fentanyl administration. Methods: From January to February 2023, we recruited people who use drugs from 34 syringe services programs across California, USA (N=999) and surveyed their substance use, health outcomes, and healthcare utilization. We compared health risks among people who injected fentanyl (78% of whom also smoked) to people who solely smoked fentanyl (n=563). Results: Of the 563 participants, forty-one percent injected fentanyl and 59% only smoked fentanyl. People who injected fentanyl were 40% more likely to have experienced a non-fatal overdose in the past 3 months (27% vs. 19%; aRR=1.40; 95% CI=1.03, 1.93) and 253% more likely to have had a skin and soft tissue infection in the past 3 months (39% vs. 15%; aRR=2.53; 95% CI=1.74, 3.67), compared to people who only smoked fentanyl. The average number of nights spent in the hospital was higher among people who injected fentanyl (average 1.2 nights vs. 0.7 nights; aIRR=1.78; 95% CI=1.02, 3.09; p=0.04).There were non-significant associations between mode of fentanyl administration and number of emergency department visits and probability of hospitalization. Conclusions: Findings suggested that people who injected fentanyl were at higher risk for overdose and skin and soft tissue infections than people who only smoked fentanyl. Distribution of safe smoking supplies may facilitate transitions from injecting to smoking fentanyl, thereby reducing health risks associated with fentanyl use.