Here is the design of a clinical trial:

Official Title: Ready2Change-Methamphetmine (R2C-M): A Randomised Controlled Trial of a Telephone-delivered Intervention to Reduce Methamphetamine Use

Included conditions:
- Methamphetamine Use Disorder

Study Armgroups:
- {'label': 'R2C-M intervention', 'type': 'EXPERIMENTAL', 'description': 'R2C-M telephone intervention - Six approximately weekly sessions of R2C-M telephone-delivered intervention (50 minutes in duration), delivered by the same R2C-M Counsellor each session (a qualified clinical psychologist trained in the R2C protocol by the developer, Dr Kate Hall). Call duration will be recorded. Sessions will be digitally recorded, and an independent researcher will randomly select and rate fidelity of intervention sessions for 20% of participants.\n\nR2C-M workbooks - Two workbooks to facilitate counsellor-delivered exercises within sessions, and between-session practice, will be mailed/emailed to participants.\n\nSelf-help booklet - (as in control group) R2C-M participants will also receive a booklet of information and self-help strategies for methamphetamine use problems.', 'interventionNames': ['Behavioral: R2C-M', 'Other: Self-help booklet']}
- {'label': 'Control', 'type': 'ACTIVE_COMPARATOR', 'description': 'Self-help booklet - Control participants will receive (by mail/email) a booklet of information and self-help strategies for methamphetamine use problems.\n\nTelephone check-ins + information on further support - (to control for frequency of contact across treatment arms) Participants in this group will receive 6 telephone calls from the research team (lasting maximum 5 minutes, call duration will be recorded). During these calls, participants will be asked about their use of the booklet. Whenever required, the researcher will provide participants with information on further support (e.g. DirectLine or other state/territory AOD helpline for advice or referral).', 'interventionNames': ['Other: Self-help booklet']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'R2C-M', 'description': 'R2C-M comprises 12 modules addressing core practice elements and skills from evidence-based cognitive and behavioural interventions. Modules include: (i) self-monitoring, goal setting and behaviour change skills; (ii) identification of strengths and motivational enhancement; (iii) relapse prevention; (iv) psychoeducation and harm reduction; (v) emotion regulation skills; (vi) anger management skills; (vii) urges and cravings management skills; (viii) sleep hygiene skills; (ix) mindfulness skills; (x) interpersonal skills; (xi) anxiety management skills; (xii) depressed mood management skills. The R2C-M workbooks contain psychoeducation and intervention exercises, to facilitate counsellor-delivered exercises within sessions, and between-session practice.', 'armGroupLabels': ['R2C-M intervention']}
- {'type': 'OTHER', 'name': 'Self-help booklet', 'description': 'A booklet of information and self-help strategies for methamphetamine use problems.', 'armGroupLabels': ['Control', 'R2C-M intervention']}

Primary Outcomes:
- {'measure': 'Methamphetamine problem severity', 'description': 'Change in methamphetamine problem severity (Drug Use Disorders Identification Test; DUDIT)', 'timeFrame': '3-months post-randomisation'}

Please estimate the sample size based on the assumption: 
The study assumes a 5% significance level, 90% power, and a 20% dropout rate. The between-subject variance component is 21, and the within-subject variance component is 63. The study also considers potential deterioration of effects by 50% at 6 months and return to baseline by 12 months.
Sample size estimates
          We aim to randomise between 188 and 204 participants to this study (i.e. total N = 196 Â± 8, subjects per study arm = 98 Â± 4). This was calculated using the Genstat [66] power procedure. The primary outcome measure (DUDIT score 3 months post-baseline) can range from 0 to 40 and will be analysed via a linear mixed model. Using data from our pilot workÂ [20], we found that the between-subject variance component in DUDIT score was 21, the within-subject variance component was 63 and the estimated improvement (decline) in DUDIT score was 17 (SE = 1.6). We estimate that by 3 months there will be an improvement of at least 16 in the R2C-M arm and that the control arm could exhibit an improvement of up to 10. With 75 evaluable subjects in each treatment arm, the study will have 90% power to detect this difference in improvement using an F-test conducted at the 5% significance level. If these conjectured improvements by 3 months are not durable and, for example, deteriorate by 50% at 6 months, and return, on average, to baseline values by 12 months, then this treatment-by-time interaction scenario will be detected with at least 90% power. The initial target sample size of 188 comprises 75 per arm, inflated to 94 per arm to allow for approximately 20% drop-out, which is based on the attrition rates reported in other treatment [67] and helpline [68] research with AOD cohorts using 12Â month endpoints. Provision has been made to increase the recruitment target, based on the 3Â and 6Â month attrition rates observed after recruitment and data collection commenced (after 12 months of data collection with this complex cohort, 3 and 6Â month attrition rates were higher than anticipated). As such, the target sample size was increased from 188 subjects, to up to 204 participants (i.e. an additional 8 subjects based on the 3Â month attrition rate; or an additional 16 subjects based on the 6Â month attrition rate). Based on our experience with social media advertising for alcohol and other drug treatment trials, it is estimated that 10â12 participants will be recruited per month over 18 months.