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

OBJECTIVES: 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).

METHODS: 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.

RESULTS: 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).

CONCLUSION: 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.