Heroin injection to fentanyl smoking: Examining temporal trends in substance type and route of administration among people who inject drugs in Los Angeles, CA and Denver, CO, USA between 2021-2022.

INTRODUCTION

In the US, fentanyl is replacing heroin in illicit drug markets. We examined temporal effects of changing substance use patterns and self-reported skin abscesses among people who inject drugs (PWID).

METHODS

We surveyed 472 PWID in Los Angeles, CA and Denver, CO during 2021/22. Survey items covered demographics, drug use patterns (type, frequency, and route of administration), injection-related risk behaviors, and self-reported skin abscesses over the last 3 months.

ANALYSIS

We used baseline data to determine if heroin and fentanyl use patterns and health outcomes changed over time. We reclassified the sample into three - 6-month participant recruitment periods (Period 1: Apr to Sep 2021 [n = 256/54 %]; Period 2: Oct to Mar 2021/22 [n = 129/27 %]; Period 3: Apr to Sep 2022[n = 87/18 %]). We used bivariable analyses to determine factors associated with daily injection of any drug, daily non-injection fentanyl use, and abscesses. Regression analyses were conducted to determine factors associated with these changing substance use patterns and abscesses.

RESULTS

We observed statistically significant changes in the following: daily injection (78 % in Period 1 to 56 % in Period 3; p < 0.001), daily heroin use (46 % in P1 to 28 % in P3;), daily fentanyl smoking (18 % in Period 1 to 33 % in Period 3) and abscesses (43 % in P1 to 32 % in). In multivariable robust Poisson regression models, participants recruited in later periods with lower risk of daily injection and abscesses and higher risk of daily non-injection fentanyl use.

DISCUSSION

Changes in the illicit opioid market have resulted in decreased injection and increased non-injection fentanyl use. Lower injection drug use may be leading to lower risk for abscesses among PWID.