Table 2.

Multivariable Multinomial Logistic Regression Analysis Comparing Risk Factors for Injection or Smoking or Inhalation Abuse As Usual Route of Abuse Compared to Oral Abuse among Primary Prescription Opioid Abuse Treatment Admissions, United States, 2004–2013.

	Injection Abuse versus Oral Abuse	Smoking or Inhalation Abuse versus Oral Abuse
Characteristic	Relative Risk Ratio (95% Confidence Interval)	Relative Risk Ratio (95% Confidence Interval)
Year
2004	Ref	Ref
2005	0.96 (0.92–1.00)	1.15 (1.10–1.19)*
2006	0.92 (0.88–0.96)*	1.26 (1.22–1.31)*
2007	0.82 (0.79–0.86)*	1.16 (1.12–1.20)*
2008	0.90 (0.87–0.94)*	1.22 (1.18–1.26)*
2009	1.05 (1.01–1.09)*	1.38 (1.34–1.43)*
2010	1.26 (1.22–1.31)*	1.65 (1.60–1.70)*
2011	1.34 (1.30–1.39)*	1.74 (1.69–1.80)*
2012	1.45 (1.40–1.50)*	1.74 (1.69–1.80)*
2013	1.77 (1.71–1.83)*	1.77 (1.72–1.83)*
Sex
Female	Ref	Ref
Male	1.38 (1.36–1.40)*	1.35 (1.34–1.37)*
Age, years
12–17	Ref	Ref
18–24	2.85 (2.68–3.04)*	1.00 (0.96–1.03)
25–34	2.16 (2.03–2.30)*	0.56 (0.54–0.58)*
35–44	1.60 (1.50–1.71)*	0.37 (0.36–0.39)*
45–54	1.33 (1.24–1.42)*	0.25 (0.24–0.27)*
55 and over	1.07 (0.98–1.15)	0.20 (0.19–0.21)*
Race/Ethnicity
Hispanic	Ref	Ref
Non-Hispanic White	1.44 (1.40–1.49)*	1.41 (1.37–1.44)*
Non-Hispanic Black	0.57 (0.54–0.60)*	1.01 (0.98–1.05)
Non-Hispanic Other	1.70 (1.62–1.77)*	2.44 (2.36–2.53)*
Living Arrangement
Independent	Ref	Ref
Dependent	1.27 (1.25–1.29)*	1.05 (1.04–1.07)*
Homeless	1.73 (1.69–1.77)*	1.14 (1.12–1.17)*
Employment Status
Full-time employment	Ref	Ref
Part-time employment	1.28 (1.24−1.32)*	1.05 (1.03–1.08)*
Not in labor force	1.37 (1.34–1.40)*	0.92 (0.90–0.93)*
Unemployed	1.69 (1.65–1.72)*	1.07 (1.06–1.09)*
U.S. Census Region
Northeast	Ref	Ref
Midwest	1.65 (1.62–1.68)*	0.47 (0.46–0.48)*
South	2.15 (2.12–2.19)*	0.70 (0.69–0.70)*
West	0.89 (0.87–0.91)	0.52 (0.51–0.53)*
Number of Prior Substance Abuse Treatment Episodes
0	Ref	Ref
1	1.18 (1.17–1.20)*	1.04 (1.03–1.05)*
2	1.44 (1.42–1.47)*	1.06 (1.04–1.07)*
3 or more	1.79 (1.76–1.82)*	1.02 (1.00–1.03)*
Age of First Use of Prescription Opioids, years
Less than 14	Ref	Ref
15–17	0.99 (0.96–1.01)	1.07 (1.04–1.09)*
18–20	0.85 (0.83–0.87)*	1.05 (1.03–1.07)*
21–24	0.74 (0.72–0.76)*	0.97 (0.95–0.99)*
25–29	0.65 (0.64–0.67)*	0.86 (0.84–0.88)*
30–39	0.58 (0.57–0.60)*	0.79 (0.77–0.81)*
40 and over	0.44 (0.42–0.46)*	0.72 (0.69–0.74)*
Substance Reported At Admission±
Alcohol	0.87 (0.85–0.88)*	0.92 (0.91–0.93)*
Cocaine or Crack	1.71 (1.68–1.74)*	1.29 (1.27–1.31)*
Marijuana	1.09 (1.07–1.10)*	1.27 (1.25–1.28)*
Heroin	1.88 (1.84–1.92)*	1.48 (1.46–1.51)*
Methamphetamine	2.21 (2.15–2.26)*	0.95 (0.92–0.98)*
Benzodiazepines	0.98 (0.96–1.00)*	1.02 (1.01–1.04)*