Table 2 Analyses, Outcome Measures, and Main Findings of Included Studies

Krawcyk et al. [33]

1) Multivariate logistic regression and sensitivity analysis

2) Multivariate accelerated time failure model

Retention in MOUD beyond 6 months, based on TEDS length of stay in days

Age

Race/ethnicity

Education

Employment

Housing

Veteran Status

Prior month arrest

Age of first use

Frequency of use in prior month

Primary opioid use

Comorbid psychiatric problem

Referral source to treatment

Other substance use (alcohol, marijuana, benzos, cocaine, methamphetamine)

Comorbid methamphetamine use was associated with lower odds of 6 month treatment retention (Odds Ratio [OR]: 0.48 [95% CI 0.45–0.51]), and shorter 6 month treatment retention (Time Ratio [TR]: 0.64 [95% CI 0.61–0.66]), as well as lower odds of 12 month treatment retention (OR: 0.38 [95% CI 0.35- 0.41]) and shorter 12 month treatment retention (TR: 0.58 [95% CI 0.55–0.60])

Comorbid methamphetamine use was the strongest predictor of shorter MOUD treatment retention, and was strongly associated with lower odds of 6 month and 12 month MOUD retention

Liu et al. [38]

1) Cox regression models to predict drop-out

2) Log-binomial regression models to predict poor adherence

Drop-out of MMT: not having visited the clinic for at least 30 consecutive days prior to the study’s completion date

Poor-adherence to MMT: either drop-out case or having attended MMT clinic for less than 50% of the follow-up period to cover intermittent MMT

Gender

Age

Education level

Marital status

Employment status

HIV infection status

Drug use history

MMT history

Those who used methamphetamine in the past 6 months had a higher likelihood of MMT treatment dropout(

Adjusted Hazard Ratio [aHR]: 2.26 [95% CI 1.15–4.43])

Patients who had used methamphetamine or any kind of club drugs in the last 6 months were 2.26 times more likely than others to drop out from MMT

Lo et al. [37]

1) Pearson’s Chi-Square for categorical variables

2) Mann–Whitney rank sum for continuous variables

3) GEE analyses

Self-reported MMT discontinuation in the last 6 months, defined as accessing methadone at one visit, and not being on methadone at a subsequent visit

Age

Gender

Race

Homelessness status

HIV status

Substance use history (alcohol, crack cocaine, opioids, heroin, cocaine)

MMT history

Those who used methamphetamine daily were more likely to discontinue MMT treatment (OR:1.75 [95% CI 1.07–2.85])

Daily methamphetamine use was associated with 1.75 times likelihood of MMT discontinuation

Mackay et al. [34]

1) Poisson distribution

2) Chi-squared and Wilcoxon Rank Sum

3) Kaplan–Meier to determine probability of methadone discontinuation

(4) Bivariable and multivariable Cox regression models

Time to discontinuation of methadone, defined as not being on methadone at the time of a follow-up interview during study period

Age

Gender

Self-identified ancestry

HIV serostatus

Incarceration history

Living in the downtown east side(DTES)

Homelessness history

Other substance use (opioid, cocaine, crack, alcohol)

Methadone history

Those who reported more than weekly methamphetamine use were more likely to discontinue treatment (aHR: 1.38 [95% CI 1.03–1.85])

In a sub-analysis, compared to no methamphetamine use, all routes of administration of methamphetamine were significantly associated with methadone discontinuation: both injection and non-injection (HR: 1.97 [95% CI 1.40–2.77]), non-injection only (HR: 1.85 [95% CI 1.20–2.86), and injection only (HR: 1.75 [95% CI 1.29–2.38])

Compared to no methamphetamine use, at least weekly methamphetamine use was independently associated with higher rates of methadone discontinuation. All routes of administration of methamphetamine were significantly associated with methadone discontinuation

Pilarinos et al. [36]

(1) Chi-squared

(2) Mann–Whitney

(3) Bivariate and multivariable Cox regression models

Time to any MMT discontinuation, defined as individuals who indicated they had received MMT in the last 6 months but were not currently on MMT

Age

Age of first drug use

Sex

Race (Indigeneity)

Ethnicity

Depression

Child welfare involvement

Childhood adverse events

MMT initiation period

Recent living in downtown east side (DTES)

Recent drug use

Recent employment

Recent homelessness

Recent incarceration

Recent non-pharmacological treatment

Recent difficulty accessing services

Those who reported recent weekly crystal methamphetamine use were more likely to discontinue treatment (aHR: 1.67 [95% CI 1.19–2.35])

In sub-analyses, recent weekly crystal methamphetamine use was also positively associated with ‘actionable’ MMT discontinuation in adjusted analyses (aHR = 4.61 [95% CI 1.78–11.9])

Self-reported weekly use of crystal methamphetamine is associated with an increased likelihood of MMT treatment dropout, as well as ‘actionable’ dropout (i.e., reason for dropout that can be addressed through policy or guideline changes)

Tsui et al. [35]

(1) Kaplan–Meier survival curves to assess association between methamphetamine use and time to discharge

(2) Cox proportional hazards regression used to estimate the relative hazards for treatment discharge

Survival time defined as time from buprenorphine induction/enrollment to earliest date of discharge

Primary outcome: time to buprenorphine treatment discharge (if no active prescription for buprenorphine and no contact with program for > 30 days)

Age

Gender

Clinic site

Period of enrollment in treatment

Race

Ethnicity

Education level

Non-methamphetamine substance use

Previous treatment history

Those with past-month methamphetamine use at baseline were more likely to drop out of buprenorphine treatment (HR: 2.39 [95% CI 1.94–2.93]); the risk increased with additional days of methamphetamine use:

1–10 days (HR:2.05 [95% CI1.63–2.57]); 11–20 days (HR: 3.04 [95% CI2.12–4.23]); 21–30 days (HR: 3.61 [95% CI 2.40–5.23])

Methamphetamine use is associated with increased risk of non-retention for patients who are treated for OUD with buprenorphine. The risk increases with additional days of methamphetamine use

Vafaeinasab et al. [39]

(1) Chi-square test and survival analysis

(2) Log-rank and Kaplan–Meier curves

Methadone consumption and therapy/discontinuation of treatment recorded by physician or consultant;

Therapy survival rates calculated at first, third, and 6 months

Gender

Relationship with family/family support

Age

Treatment history

Substance use history

Physical and mental illness history

A lower proportion of individuals who had positive urinalysis for methamphetamine were retained in methadone at 6 months, however, findings were not significant due to low sample size. A total of 14.8% of individuals who had at least one positive test of methamphetamine use continued treatment for up to 6 months, compared to 30.2% of individuals who did not test positive for methamphetamines

Patients with at least one positive test for methamphetamine use during treatment period experienced lower rates of retention in treatment

Banta-Green et al. [48]

(1) Bivariate statistics (chi-squared and t-tests)

(2) Logistic regression model

12 month treatment retention, defined as remaining in treatment at day 366 following admission to MMT

Age

Marital status

Educational status

Race

Public assistance type

Medical severity/psychiatric severity composite score

Housing status

Current legal involvement

Drug use at time of intake

Those who reported methamphetamine were less likely to be retained in MMT treatment at 12 months

(OR:0.62 [95% CI 0.44–0.89])

Methamphetamine use was significantly associated with decreased odds of MMT retention