Table 1 Demographic and clinical data in the study participants and comparisons between the groups with and without reported subjective opioid withdrawal symptoms

Gender, female/male^b

27/56 (33/67)

15/30 (56/54)

12/26 (44/46)

0.865

Age, years^c

45 (9, 26–66)

45 (9, 26–62)

44 (10, 26–66)

0.493

Methadone dose, mg/day^c

97 (24, 20–170)

101 (24, 35–170)

92 (23, 20–150)

0.079

Methadone serum concentration, ng/mL^c

374 (188, 74–1005)

347 (168, 113–1005)

405 (208, 74–998)

0.145

CDR,^d (ng/mL)/(mg/day)^c

4 (2, 1–11)

3 (2, 1–11)

4 (2, 1–9)

0.039

Time since last dose, hours^c

21 (8, 0–28)

22 (5, 1–28)

19 (10, 0–27)

0.199

Duration of opioid agonist treatment^c

9 (5, 1–20)

9 (5, 1–18)

9 (5, 1–20)

0.922

Direct observed treatment, day/week^c

4 (2, 1–7)

4 (2, 1–7)

3 (2, 1–6)

0.026

Self-reported substance use last month^b

73 (88)

41 (92)

32 (83)

0.187

Heroin^b

10 (12)

5 (12)

5 (13)

0.971

Other opioids^b

5 (6)

3 (6)

2 (5)

0.819

Benzodiazepines^b

50 (62)

29 (64)

21 (55)

0.233

Cannabis^b

55 (66)

30 (65)

25 (67)

0.828

Amphetamine^b

26 (31)

15 (33)

11 (30)

0.789

Alcohol^b

38 (46)

22 (49)

16 (42)

0.542