. 2019 Mar 4;14(3):e0213357. doi: 10.1371/journal.pone.0213357

Table 2. Patterns of drug use and median age of initiation and median years to injection by birth cohort and recruitment period.

	2005–2008 recruitment period		2015–2018 recruitment period
	Median age of illicit drug initiation (IQR)
	Born before 1980 (n = 919)	Born 1980 or later (n = 89)	Born before 1980 (n = 539)	Born 1980 or later (N = 198)
Prescription opioids	17 (15–18)	15 (14–17)^**	16 (12–25)	16 (13–17)
Prescription non-opioids	17 (16–18)	15 (11–16)	16 (14–18)	14 (11.5–17)^*
Prescription drugs^a/non-injection illicit drugs	18 (16–20)	16 (15–17)	16 (15–18)	16 (15–17)
Non-injection illicit drugs	18 (16–21)	15 (13–16)^***	17 (15–19)	16 (15–18)^**
Injection only^b	18 (16–22)	15 (14–16)^***	18 (16–23)	16.5 (15–19)^*
	Median years to injection initiation (IQR)
	Born before 1980 (n = 508)	Born 1980 or later (n = 68)	Born before 1980 (n = 357)	Born 1980 or later (n = 172)
Prescription opioids	5 (2–10)	3.5 (2–5)	5 (3–13)	6 (2–7)
Prescription non-opioids	6 (2–10)	4 (2–4)	7 (3–13)	8 (4–10)
Prescription drugs^a/non-injection illicit drugs	4 (2–7)	2 (1–4)	5 (3–12)	4 (3–7)
Non-injection illicit drugs	5 (2–10)	3 (1–5)^**	7 (4–13)	6 (3–9.5)^*
	Median number of drugs used prior to injection initiation (IQR)
	Born before 1980 (n = 504)	Born 1980 or later (n = 68)	Born before 1980 (n = 348)	Born 1980 or later (N = 160)
Prescription opioids	2 (1–4)	5 (3–6)^**	3 (2–4)	5 (1–7)
Prescription non-opioids	2 (1–3)	3 (2–7)	3 (2–5)	5 (4–7.5)^**
Prescription drugs^a/non-injection illicit drugs	4 (3–5)	4 (2–6)	4 (3–6)	6 (4–7)
Non-injection illicit drugs	2 (1–3)	3 (2–6)^***	3 (2–4)	5 (2–6.5)^***

a. either prescription opioid or non-opioid

b. Median age to first injection drug use since injection drug use preceded or occurred at the same age as non-injection drugs in this group

Boldface indicates statistical significance difference within each recruitment period

*p<0.05

** p<0.01

*** p<0.001