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Reach and effectiveness of mailed nicotine replacement therapy for smokers: 6-month outcomes in a naturalistic exploratory study
  1. Laurie Zawertailo1,2,
  2. Rosa Dragonetti1,
  3. Susan J Bondy3,4,
  4. J Charles Victor4,5,
  5. Peter Selby1,3,4,6,7
  1. 1Addictions Program, Nicotine Dependence Clinic, Centre for Addiction and Mental Health, Toronto, Ontario, Canada
  2. 2Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
  3. 3Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
  4. 4Ontario Tobacco Research Unit, Toronto, Ontario, Canada
  5. 5Institute of Health Policy Management and Evaluation, Toronto, Ontario, Canada
  6. 6Department of Family and Community Medicine, University of Toronto, Toronto, Ontario, Canada
  7. 7Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada
  1. Correspondence to Dr Peter Selby, Director, Addictions Program, Centre for Addiction and Mental Health, 33 Russell Street, Toronto, ON M5S 2S1, Canada; peter_selby{at}camh.net

Abstract

Background There are important inequities in smoker access to clinic-based smoking cessation services. Low barrier high-reach interventions are proposed as solutions to these inequities. Although effective, telephone quitlines, which provide multi-session counselling but no medication, have low utilization with high attrition. The objective of this study was to determine the effectiveness of free nicotine replacement therapy (NRT), brief advice and self-help materials on quit attempts and 6-month quit rates in motivated smokers.

Methods In this open-label naturalistic study, 14 000 treatments of 5 weeks in duration of either nicotine patch (n=10 000) or nicotine gum (n=4000) were made available to all eligible adult smokers in Ontario, Canada, who called a toll-free number to register with the STOP (Smoking Treatment for Ontario Patients) Study and receive a single brief intervention. The primary outcome measure was self-reported abstinence rates at 6 months post-treatment among STOP participants. These data were compared with quit rates that were reported in a concurrent no-intervention cohort of Ontario smokers matched for eligibility.

Results 16 405 callers were assessed and 13143 eligible participants were mailed a treatment package with 5 weeks of NRT (choice of patch or gum), self-help and community resource materials. Among the 6261 participants who consented to follow-up, 2601 (42%) had complete follow-up data. Of those with complete follow-up data, the percentage reporting abstinence after 6 months in the treatment cohort was 21.4%, relative to 11.6% in the no-intervention cohort (rate ratio of 1.84; 95% CI 1.79 to 1.89), with the 30-day point prevalence of 17.8% and 9.8% for the intervention and no-intervention cohorts, respectively (rate ratio 1.81; CI 1.75 to 1.87).

Conclusions Provision of free NRT by mail following a brief telephone intervention is an effective strategy to reach and assist a large number of smokers making a quit attempt.

  • Nicotine replacement therapy
  • smoking cessation
  • cessation
  • addiction
  • co-substance use
  • priority/special populations
  • primary healthcare
  • prevalence
  • environmental tobacco smoke
  • cessation
  • health services
  • smoking caused disease
  • concurrent mental health and addiction
  • harm reduction

http://dx.doi.org/10.1136/tobaccocontrol-2011-050303

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    Introduction

    Evidence-based treatment for tobacco dependence requires a combination of counselling and pharmacotherapy, such as nicotine replacement therapy (NRT).1–3 To provide additional benefit, behavioural support is recommended in combination with pharmacotherapy. However, many smokers cannot be reached through cessation treatment offered in clinical settings due to smoker, clinician and system-level barriers.4–6 Therefore, the real world impact of these clinic-based interventions (increased number of ex-smokers) has been modest.

    Making NRT widely available to smokers with minimal barrier to access is also recommended as a fundamental public health measure.7 However, providing NRT without prescription has had limited effect on increasing use of the product,8 and cost remains a significant barrier to using NRT to aid in smoking cessation.9 Efforts to increase the reach of counselling have led to the development of telephone quitlines and web-based tobacco interventions and have made them a standard of the FCTC Article 14.10

    One strategy to increase the appropriate use of NRT has been to provide it for free to motivated smokers as a population-wide intervention strategy while combining it with counselling.11–14 These programmes demonstrated that free NRT resulted in increased volume of calls to the quitline, a high percentage of quit attempts and good abstinence rates at 6- and 12-month follow-up time points, although these studies lacked appropriate comparator arms.12 ,14–16

    To maximise the reach to smokers across Ontario, we developed a pragmatic programme that provided 5 weeks of NRT (patches or gum) to the first 14 000 eligible smokers to call a toll-free quitline. We compared outcomes with a non-intervention cohort of randomly selected sample of smokers in Ontario being studied simultaneously.17 ,18 In this report, we present key cessation outcomes at 6 months and estimate the increase in cessation rates attributable to the treatment provided.

    Methods

    Intervention arm—the STOP giveaway and follow-up

    The Smoking Treatment for Ontario Patients (STOP) programme was launched in January 2006. Region-specific media promotion was used to increase the reach in more remote regions of the province with a high prevalence of smoking. Following media announcements, the call centre received over 7500 calls within the first 24 h.

    Participants and retention

    Inclusion criteria were Ontario residents 18 years of age and older who smoked at least 10 cigarettes per day and were willing to make a quit attempt within 30 days. Exclusion criteria were contraindications to NRT: pregnancy, lactation, recent heart attack or cardiovascular incident. Of 16 405 callers, 13 158 were eligible for the intervention and 13 143 received it (figure 1). Consent to participate in the follow-up was included in the recruitment materials only after the first 6882 sequential participants had been enrolled. After this point, all new participants were asked to consent to follow-up at the time of initial recruitment, and all these participants (N=6261) provided initial consent to the follow-up. Of these, 5347 were successfully contacted at 6 months for follow-up (participants were deemed ‘Not able to contact’ after three follow-up attempts); 2746 refused to participate in the follow-up and 2601 responded, representing a response rate of 41.5% (respondent response rate of 48.6%).

    Figure 1
    Figure 1

    Flow chart of recruitment and follow-up for recipients of nicotine treatment therapy (NRT) in the Smoking Treatment for Ontario Patients (STOP) Study.

    Intervention procedures and baseline measures

    An automated voice system screened caller eligibility, provided study information and obtained consent. A live agent then completed a computer-guided brief assessment based on the minimal data set used by the North American Quitline Consortium.19 Participant demographic characteristics were collected and detailed measures of smoking history, current smoking behaviour and the Heaviness of Smoking Index (HSI).20 Other health status measures included current alcohol use and self-report of past and present diagnosis of psychiatric illness. The assessment questionnaire also served as a modified ‘5A intervention’,2 whereby callers were asked about their smoking; assessed with respect to stage of change, motivation and importance of quitting smoking and advised on type of NRT to use. Those eligible for NRT were couriered a kit containing 5 weeks of NRT, self-help materials, a toll-free telephone hotline for questions and concerns and the provincial telephone quitline number to access additional counselling if desired.

    Outcome assessment

    Three major outcomes were examined according to the recommended outcome definitions for smoking cessation clinical trials and population-level studies.21 All outcomes were based on self-report data at the 6-month follow-up interview. The primary outcome was whether or not the participant was smoking at the time of the 6-month interview, with cessation defined as not smoking at the date of the interview and having not smoked, not even a puff for at least the past 30 days. Secondary outcome measures included a serious quit attempt that was defined as having stopped intentionally, for 1 day or longer, at any time during the 6-month period and self-reported quit without meeting the 30-day point prevalence criteria.

    Population control arm (Ontario Tobacco Survey)

    The study control arm was obtained from the longitudinal follow-up study of smokers in the contemporaneous Ontario Tobacco Survey (OTS) project. The OTS smoker's cohort was a panel follow-up study of a population-representative random sample of Ontario residents aged 18 years and older who had smoked within the past 6 months at baseline. Baseline recruitment extended from July 2005 through December 2008, with first 6-month follow-up for the entire cohort completed in March 2009. The OTS design22 and its representativeness have previously been described.17 ,18

    OTS participants were interviewed by telephone every 6 months for a minimum of 2 years. Data used here are from the baseline and first follow-up interviews. Participant demographic data and detailed smoking history were obtained using comparable measures as for the STOP. The use of NRT prior to the baseline interview and during the first 6-month follow-up period was documented.

    To evaluate the STOP intervention, a subcohort of the OTS panel (n=4501) was generated matching the smoking behaviour and quit intention criteria for STOP, cited above. Specifically, OTS respondents had to report smoking at least 10 cigarettes per day and report an intent to quit within the next 30 days. Of the 995 OTS participants who met STOP criteria, 908 could not have received NRT from the STOP initiative (figure 2). Of these, 780 had complete outcome data at the 6-month follow-up (85.9% retention). Outcome measures were the same as for the STOP study.

    Figure 2
    Figure 2

    Flow chart of recruitment and follow-up for a subset of the Ontario Tobacco Survey matched for eligibility criteria to Ontarians participating in the Smoking Treatment for Ontario Patients (STOP) Study.

    Ethical approvals

    Research ethics board approvals for the STOP study and OTS were obtained from the Centre for Addiction and Mental Health and the Universities of Toronto and Waterloo, Ontario, respectively.

    Analysis

    Baseline demographic and smoking characteristics for STOP participants were compared with population-based estimates of smoker characteristics in the OTS study. Within each arm, we examined baseline smoker characteristics and behaviour as predictors of smoking cessation to describe associations and to identify potential control covariates when contrasting the two arms. Regression analyses used the Log-binomial regression model.23 ,24 Models' diagnostics were performed for assumptions and multi-collinearity.

    In these analyses, the OTS cohort making up the comparator arm was restricted to smokers matching STOP inclusion criteria and was re-weighted by age and sex to match the STOP intervention arm. Study outcome rates are presented per arm, as cessation rate ratios (RR) and rate differences (RD) contrasting the two arms. Variance estimates for the OTS arm were appropriate to the stratified sampling design and weighting using Taylor-Series variance estimation. Wald CIs for RR and RD estimates were obtained using the first Taylor-series expansion using variance estimates calculated separately for each arm.25 ,26

    Two methods were used to address the possible impact of loss to follow-up as a source of bias in comparing cessation rates between STOP and OTS. First, we applied a single-imputation method in which all participants lost to follow-up were assumed to still be smoking.27 For variance estimation, the sample size was based on the number of respondents to the follow-up survey as suggested by Higgins et al.28 Second, a multiple imputation method to account for differential loss to follow-up was employed. Sets of randomly generated imputed values were generated for each missing 6-month follow-up outcome datum, in each arm, using the logistic regression method to fit the probability of the outcome, among missing observations, based on predictors of missing status and cessation among complete cases.29 Predictor variables used in the imputation process for the STOP arm were those presented in table 1. For the OTS arm, the same predictors were used minus alcohol use and mental health comorbidity that were not available.

    View this table:
    Table 1

    Characteristics of Ontario smokers participating in the Smoking Treatment for Ontario Patients (STOP) nicotine replacement therapy giveaway at baseline and conditional on complete 6-month follow-up

    In all STOP-OTS comparison analyses, the potential impact of co-intervention (during the time period when Ontario residents could have participated in both the OTS and the STOP quit-line giveaway) was considered. Analyses were repeated using the entire OTS cohort, as well as restricted to OTS participants observed before or after the STOP study mass recruitment campaign. All analyses were conducted in SAS V.9.1.3.

    Results

    Characteristics of STOP intervention participants

    Demographic characteristics and smoking behaviour of the STOP participants appear in table 1. The majority smoked >20 cigarettes per day or within 30 min of waking. Twelve per cent, 48% and 40% of respondents had low (0–2), moderate (3–4) and high (5–6) HSI scores, respectively, consistent with the inclusion criteria.

    Compared with all adult Ontario smokers (OTS cohort not restricted to STOP eligibility criteria), STOP participants were more likely to be daily smokers and have a high HSI score, more likely to be women (59% vs 54%) and more likely to have less than high school education. Relative to all smokers in Ontario, STOP participants had higher prevalence of psychiatric comorbidities regardless of smoking status.30

    Baseline characteristics of those with and without complete 6-month follow-up interview data are also presented in table 1. STOP participants who completed the 6-month interview were more likely to be older, women, have current psychiatric comorbidity and be less heavy alcohol users. With the exception of a 5-year average age difference between those with and without 6-month follow-up data, differences were small in magnitude but were statistically significant, given the large sample size (n=5347). Those lost to follow-up had lower incomes, higher alcohol intake levels and were more likely to report current psychiatric symptoms, although these differences were small.

    Among OTS participants matching STOP eligibility, 21.0% reported use of NRT, 12.8% reported having used any form of behavioural supports for smoking cessation (including advice from a physician, self-help materials or individual or group-based behavioural support) and 4.4% reported both, during the first 6 months of follow-up. There was no observed difference in the reported rate of NRT use among OTS participants studied during versus outside the time period for the STOP giveaway.

    Predictors and rates of smoking cessation outcomes at 6 months

    In STOP, 67.4% reported having made at least one serious attempt to quit smoking between receipt of their NRT and before the 6-month follow-up interval; 21.4% reported quitting smoking at the time of the interview and 17.8% were neither smoking at the time of the 6-month interview nor had smoked (not even a puff) within the previous 30 days (table 2).

    View this table:
    Table 2

    Associations between quit attempts, self-reported quit at time of interview and prevalence of 30-days abstinence at 6-month follow-up quit period prevalence and past quit attempts with characteristics of Smoking Treatment for Patients (STOP) study participants

    In bivariate analyses, type of NRT received, sex, age, income, alcohol use, psychiatric diagnosis and HSI all demonstrated some association with quit attempts and self-reported 30-day abstinence at follow-up (table 2). Only education was not statistically related to any of the outcomes examined. Table 3 presents the results of three multivariable regressions that simultaneously examined the predictors of cessation outcomes at the 6-month time point. In the adjusted models predicting 30-day quit outcome, participants who had received NRT in patch as opposed to gum form, had lower HSI scores, lower alcohol intake and an absence of reported psychiatric comorbidity were more likely to have quit (table 3). Within the criteria-matched, age- and sex-adjusted OTS cohort, education, income and HSI score were all unrelated to cessation outcomes (data not shown).

    View this table:
    Table 3

    Results of log-binomial regression models (fully adjusted) presenting APR and examining predictors of cessation outcomes among participants in the Smoking Treatment for Ontario Patients (STOP) nicotine replacement therapy giveaway intervention

    Comparison of outcome rates in the intervention and control arms

    Table 4 summarises the cessation outcomes based on 30-day point prevalent abstinence contrasting the observed cessation rates in the STOP study, relative to matched and adjusted outcome rates in the OTS cohort. Using complete data (table 4, section A), the percentage of STOP participants reporting abstinence at the 6-month interview was 21.4% compared with 11.6% in the OTS estimates (a RD of 9.78%; 95% CI 6.40% to 13.15%) or an 84% likelihood of quitting in the STOP Study relative to the control arm (RR of 1.84; 95% CI 1.79 to 1.89). Results were similar when the outcome was defined as being a non-smoker for 30 days at the 6-month follow-up, with a RR of 1.81 (95% CI 1.75 to 1.87) and a 79% higher rate of cessation (95% CI 4.75 to 11.17) than expected from the OTS data.

    View this table:
    Table 4

    Comparison of smoking cessation outcome rates in the STOP nicotine replacement therapy giveaway intervention and the population-based OTS cohort of Ontario smokers. Outcome rates, RR and rate differences, with 95% CIs

    Data provided in sections B and C of table 4 present analyses considering the impact of loss to follow-up on effect estimates. Using the single-imputation method, estimated cessation rates were lower in the STOP arm, and this analysis estimated no benefit of the NRT giveaway over the control arm.

    When outcome rates were re-estimated using multiple imputations, estimated cessation rates in the STOP arm were somewhat higher than those observed from complete non-missing information (table 4, section A). These analyses indicated a statistically significant increase in cessation rates attributable to the NRT giveaway.

    Table 4 also presents the sensitivity analysis where the analyses were repeated using only OTS participants studied while the STOP intervention was not offered, which had little effect on the estimates.

    Cost-effectiveness of the intervention arm

    In order for the intervention within the STOP arm to be practical for implementation at the public health level, it should be shown to be cost-effective in addition to efficacious. Calculation of the costs associated with the implemented STOP programme resulted in the average cost per caller approximately $C179, with the cost per quitter approximately $C1720 (intention to treat (ITT) self-reported quit rate of 10.4% at 6 months).

    Discussion

    This exploratory study demonstrated that an initial brief intervention plus 5 weeks of free NRT to motivated smokers in Ontario with completer follow-up data significantly increased self-reported 6-month abstinence rates compared with our no-intervention control arm who did not receive any free NRT, materials or advice to quit. This initiative is one of few phone- and mail-based NRT programmes to compare long-term cessation rates in an intervention cohort to a no-intervention cohort. This study also evaluated the largest population-wide smoking cessation intervention provided across urban, rural and remote areas. This is important because rural and remote areas of Ontario are under serviced with respect to primary healthcare.

    There have been several other evaluations of mailed NRT programmes,11–15 ,31 demonstrating that free NRT resulted in increased calls to the quitline, a high percentage of quit attempts and good abstinence rates at 6- and 12-month follow-up time points. However, they either lacked a comparison group that did not receive any intervention or the comparison group was not appropriate.12 ,14 For example, in the New York State programme, abstinence rates at 6 months were compared with that in a small group of participants who were expecting but never received their NRT in the mail.13 Not surprisingly, less than one-third of this group responded to the 6-month survey and only 10 people reported being quit at that time. In another publication using data derived from the same giveaway programme, 12-month cessation outcomes were compared with a historical cohort who called the quitline prior to the availability of free NRT, and so the participants in each arm were recruited at two different time points.11 While our study lacked a placebo arm and was not randomised to treatment versus no-treatment groups, we were able to compare our study sub-population to the sub-population from another study that was conducted concurrently and recruited subjects from the same general population of Ontario smokers.

    Outcome rates of those that completed the STOP study intervention are within the range of cessation rates observed in other large-scale non-clinical distributions or giveaway programmes, which vary in treatment intensity. For example, in the New York State study where free NRT plus counselling was made available to 35 000 smokers, the 6-month quit rate among respondents to the survey was 31% for women and 29% for men.13 In a smaller scale open-label study, 6 weeks of free patches and a self-help booklet distributed in a shopping mall to 223 smokers, there was a 6-week quit rate of 21% and a 6-month quit rate of 22% with 12% of participants reporting abstinence at both 6 weeks and 6 months.32 Our 6-month quit rate among respondents was 20% for women and 24% for men with a 5-week treatment of either nicotine patch or gum and no counselling phone calls beyond baseline. Therefore, quit rates at 6 months post-treatment in our study are in keeping with what has been reported in the literature for similar distribution programmes with more intensive counselling. Our slightly lower quit rates may be explained by a single session of counselling and the type of smoker reached through this programme, who tended to be older, female, less-educated heavier smokers with a high prevalence of psychiatric co-morbidities. These are all characteristics that predict difficulty in quitting smoking or remaining abstinent.

    A limitation of our study was a low response rate to the 6-month follow-up for our study. At approximately 42%, the response rate to our follow-up survey was lower than that of the New York City study (60%),13 and this may account for the lower outcome rates in our study when applying the imputation approach which assumes that all participants lost to follow-up have a negative outcome. However, response and follow-up rates well below 50% are not uncommon with population-based recruitment33–35 and intervention studies with minimum contact.36 Differences in missing data rates between the STOP and OTS were largely unavoidable in the concurrent but separate designs. Modest remuneration is now quite standard for population surveys,37 ,38 and OTS participants were remunerated $C15 CAD per interview. This was neither feasible for the large STOP study nor is this a realistic feature of a broadly based public health intervention. More intensive follow-up efforts and ongoing contact might increase retention rates but again are neither feasible nor desirable as a design feature to evaluate a programme for which minimum contact is an inherent feature. Despite the lower observed response and quit rates, the STOP programme intervention proved to be quite cost-effective as the average cost per caller was $C179, with an average cost per quit $C1720, providing significant value for the intervention provided. An important caveat regarding the cost-effectiveness of the STOP programme is the timeframe within which the intervention was implemented. The STOP programme was able to reach a large number of smokers in Ontario within the short timeframe of approximately 1 month and as such did not require sustained infrastructure, an aspect of the programme that may be appealing to public health officials.

    As discussed elsewhere,27 ,39 to assume that participants lost to follow-up are smoking yields overly conservative estimates in terms of minimising estimated cessation rates within one group, but the impact on relative rates across comparison groups will vary in both direction and magnitude of impact depending on relative amounts of missing data. These methods were developed in settings where greater loss to follow-up was in the non-intervention arm and are known to be inappropriate where there is a large difference in missing data between arms. In the present study, this method severely biased the results towards the null hypothesis—a conclusion which was not supported using a reasonable alternative approach, based on multiple imputation methods. Other giveaway programmes have reported single-imputation results. For example, An et al 15 also had lower response rates among NRT recipients, relative to the participants not receiving NRT, although the response RD is less marked and ITT findings for 7-day cessation remain significant.

    Multiple imputation methods have similarly been applied to cessation trials in non-clinical settings27 ,36 ,39 and have been used to analyse data from few other large-scale nicotine patch giveaway programmes.35 ,40 Bush et al 35 in a similarly naturalistic study had low follow-up rates in both NRT and non-NRT arms and both complete data and multiple imputation findings were statistically significant. Hollis et al 40 reported on a somewhat more select study population who had previously agreed to participate in research and offered incentive for follow-up. In that study, follow-up was in the two-thirds range for all arms and results for the impact of NRT, using multiple imputation were slightly lower than using the single-imputation ITT approach, but remained statistically significant.

    Limitations of studies in this area, including ours, are the open-label design and reliance on self-report measures without biochemical validation of abstinence. However, this design matches the study objective of assessing the effectiveness of mailed distribution of NRT.

    Despite these limitations, we have shown that free NRT combined with a minimal intervention can be delivered to smokers in large numbers who want to quit without the need for face-to-face assessments. However, a need still exists for continuing efforts towards identifying effective methods that increase awareness of the quitlines, particularly in high-risk populations as well as those that are not regularly exposed to preventive health service messaging. These methods need to effectively relay the information, tools and resources available for those that are willing to make a quit attempt.

    This was a high-reach cost-effective public health measure and as such should be an integral part of comprehensive tobacco control programmes. Randomised controlled trials of this method are required to increase the evidence base for such interventions to enhance the reach and adoption of smoking cessation interventions. Such a trial is currently underway in Canada.

    What this paper adds

    • Demonstration that a pragmatic real world strategy for provision of free nicotine replacement therapy to smokers can significantly increase the number of smokers abstinent at 6 months post-treatment.

    • Provision of nicotine replacement therapy along with self-help materials via mail is an effective strategy to aid a large number of smokers within a large geographic base attempt to quit smoking.

    • Along with the nicotine replacement therapy, a single brief intervention at assessment is sufficient for many smokers wanting to quit.

    • The findings of this study can have implication on influencing delivery of smoking cessation programmes within clinical practice as well as public health policy related to smoking cessation programmes.

    Acknowledgments

    We would like to acknowledge the following individual for their contributions to this manuscript: Desmond Persad for supporting development, editorial review and formatting of this manuscript in the capacity of a medical writer.

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    Footnotes

    • Funding This study was supported by the Ontario Ministry of Health Promotion through the evaluation of the proposal for the study design and provision of funding support and resources for the study. Nicotine replacement therapy was purchased at a discounted rate from Pfizer Consumer Healthcare Canada (now McNeil Consumer Healthcare, Division of Johnson & Johnson Inc.).

    • Correction notice This article has been corrected since it was published Online First. The Competing interests statement has been updated.

    • Competing interests The contributing authors have the following disclosures: L.Z. has received speaker honoraria from Pfizer Canada Inc. and has received research funding from the Canadian Institutes of Health Research, the Canadian Tobacco Control Research Initiative, The Ontario Lung Association and Cancer Care Ontario. P.S. has received: speaker's honoraria from Schering Canada, Johnson & Johnson Consumer Health Care Canada, Pfizer Canada Inc., Pfizer Inc., Sanofi-Synthelabo Canada, GlaxoSmithKline Canada Inc., Genpharm Canada, Prempharm Canada, NABI Pharmaceuticals; and consulting fees from Schering Canada, Johnson & Johnson Consumer Health Care Canada Pfizer Canada Inc., Pfizer Inc., Sanofi-Synthelabo Canada, GlaxoSmithKline Canada Inc., Genpharm Canada, Prempharm Canada, NABI Pharmaceuticals, V-CC Systems Inc., eHealth Behaviour Change Software Company, and AstraZeneca Canada Inc. R.D. has received speaker honoraria from Pfizer Inc. S.B. and J.C.V. have no conflicts of interest to declare.

    • Ethics approval Centre for Addiction and Mental Health Research Ethics Board.

    • Provenance and peer review Not commissioned; externally peer reviewed.