Drug use generations and patterns of injection drug use: Birth cohort differences among people who inject drugs in Los Angeles and San Francisco, California.

Abstract

A robust literature documents generational trends in drug use. We examined the implications of changing national drug use patterns on drug injection histories of diverse people who inject drugs (PWID). Drug use histories were collected from 776 active PWID in 2011-13. Using descriptive statistics, we examine drug use initiation by year and birth cohort (BC) differences in drug first injected. A multivariate linear regression model of time to injection initiation ([TTII] (year of first injection minus year of first illicit drug use) was developed to explore BC differences. The first drug injected by BC changed in tandem with national drug use trends with heroin declining from 77% for the pre-1960's BC to 58% for the 1960's BC before increasing to 71% for the 1990's BC. Multivariate linear regression modeling found that shorter TTII was associated with the 1980's/1990's BC (-3.50 years; 95% Confidence Interval [CI]=-0.79, -6.21) as compared to the 1970's BC. Longer TTII was associated with being female (1.65 years; 95% CI=0.40, 2.90), African American (1.69 years; 95% CI=0.43, 2.95), any substance use treatment prior to injection (4.22 years; 95% CI=2.65, 5.79), and prior non-injection use of drug that was first injected (3.29 years; 95% CI=2.19, 4.40). National drug trends appear to influence injection drug use patterns. The prescription opiate drug era is associated with shorter TTII. Culturally competent, demographically and generationally-targeted prevention strategies to combat transitions to drug injection are needed to prevent or shorten upstream increases in risky drug use practices on a national level.