Changes in substance use during outpatient treatment for substance use disorders: a prospective Norwegian cohort study from 2016 to 2020

Table 3 Adjusted linear mixed model for the Substance Use Severity Index (SUSI)^a (N = 706)

	Effect estimates
	Coefficients (95% CI)	p-value
Substance Use Severity Index (β₀)	0.29 (0.24;0.33)	< 0.001
Time trend	0.04 (−0.05;0.13)	0.397
Baseline
Female	-0.01 (− 0.04;0.01)	0.336
Years of age:
< 30	0.00 (ref.)
30–40	−0.04 (− 0.08;0.01)	0.091
40–50	−0.03 (− 0.07;0.01)	0.190
50–60	− 0.04 (− 0.09;0.00)	0.055
≥ 60	−0.08 (− 0.14;-0.01)	0.018
Injecting substance use	0.19 (0.16;0.21)	< 0.001
Inpatient detoxification^b	0.02 (−0.03;0.08)	0.422
Predictors remain constant from baseline^c
Injecting substance use	0.01 (−0.02;0.05)	0.542
Female	−0.04 (− 0.07;0.00)	0.052
Years of age:
< 30	0.00 (ref.)
30–40	−0.07 (− 0.16;0.01)	0.098
40–50	−0.05 (− 0.13;0.04)	0.293
50–60	− 0.05 (− 0.14;0.03)	0.229
≥ 60	−0.05 (− 0.16;0.05)	0.297
Time-varying predictors from baseline^d
Inpatient detoxification	0.00 (−0.04;0.04)	0.952
Starting to inject substances	0.11 (0.07;0.15)	< 0.001

The table displays a linear mixed model analysis (Restricted Maximum Likelihood regression) evaluating the impact of inpatient intoxication, injecting substance use, age, and gender on the SUSI at baseline and from baseline (over time) among patients undergoing outpatient SUD treatment
CI Confidence Interval, OAT Opioid Agonist Therapy, cSUSI Mean Change in Substance Use Severity Index, SUD Substance Use Disorder
^aThe SUSI is a continuous variable ranging from 0 to 1, where 0 indicates no substance use and 1 indicates daily substance use for all substances (cannabis, amphetamines, cocaine, opioids, benzodiazepines, and alcohol)
^bThe value shows the difference in adjusted SUSI between “going to inpatient detoxification” and “not going to inpatient detoxification” at baseline (before detoxification)
^cInterpretation: the cSUSI per year from baseline of a constant predictor and its comparator (e.g., the cSUSI of “ongoing injecting substance use” (constant predictor) and “no ongoing inject substance use” (constant comparator) per year from baseline)
^dInterpretation: the cSUSI of a time-varying predictor and its time-varying comparator per year from baseline (e.g., the cSUSI per year of “going to inpatient detoxification” and “not going to inpatient detoxification” from baseline)

ISSN: 1747-597X