Alcohol misuse is higher in the United Kingdom (UK) Armed Forces (AF) than the general population. Previous research has shown that interventions delivered via smartphone are efficacious in promoting self-monitoring of alcohol use, have utility in reducing alcohol consumption and have a broad reach. The main objective of this participant blinded (single-blinded) Randomised Controlled Trial (RCT) is to assess the efficacy of a 28-day brief alcohol intervention delivered via a smartphone app (Drinks:Ration) in reducing weekly self-reported alcohol consumption between baseline and 3-month follow-up among veterans who drink at a hazardous or harmful level and are receiving, or have received, support for mental health symptoms in a clinical setting.

Methods: In a two-arm single-blinded Randomised Controlled Trial (RCT), a smartphone app which includes interactive features designed to enhance participant motivation and personalised messaging is compared to a smartphone app which only provides Government guidance on alcohol consumption. The trial will be conducted in a veteran population who have sought help through Combat Stress; a UK veteran's mental health charity. Recruitment, consent and data collection is performed automatically through the Drinks:Ration platform. The primary outcome is change in self-reported weekly alcohol consumption between baseline (day 0) and 3-month follow-up (day 84) as measured using the Time-Line Follow back for Alcohol Consumption; secondary outcome measures include 1) change in baseline to 3-month follow-up (day 84) Alcohol Use Disorder Identification Test score, and 2) change in baseline to 3-month follow-up (day 84) World Health Organisation Quality of Life-BREF score to assess Quality of Adjusted Life Years. Process evaluation measures include 1) app usage, and 2) usability ratings as measured by the mHealth App Usability Questionnaire. The primary and secondary outcomes will also be re-assessed at 6-month follow-up (day 168) to assess the longer-term benefits of the intervention and reported as a secondary outcome. The study will begin recruitment in September 2020 and is expected to require 12 months to complete. Study results should be published in 2022.

Alcohol misuse is common in the United Kingdom (UK) Armed Forces (AF), with the prevalence rates higher in the AF than the general population. Research indicates that the trend continues after personnel leave service ('veteran' or 'ex-serving' are used interchangeably in the UK). It has been estimated that more than 50% of those who have left the AF meet the criteria for hazardous alcohol use, a score of eight or above on the Alcohol Use Disorders Identification Test (AUDIT).

The last two decades has seen a proliferation in the use of digital technologies to support brief intervention management and treatment of alcohol misuse in the general public, yet little attention has focused forwards the AF community. In the late 1990's interventions were commonly delivered via a computer using CD-ROM-based programmes, but with the advent of the World Wide Web many new opportunities arose to harness increase reach, provide real-time monitoring, and offer personalised treatment. This includes the use of Short Message Service (SMS) which have been shown to be effective in encouraging people to change their behaviour.

The aim of this Randomised Controlled Trial (RCT) is to assess the efficacy of a 28-day brief alcohol intervention delivered via a smartphone app (Drinks:Ration) in reducing self-reported weekly alcohol consumption between baseline and 3 months (day 84) among veterans who drink at a hazardous or harmful level and are receiving, or have received, support for mental health symptoms in a clinical setting.

Inclusion Criteria:

• Participants will be included if they have downloaded the app onto an iOS or Android device;
• Participants will be included if they are 18 years of age or older;
• Participants will be included if they live in the UK;
• Participants will be included if they consume fourteen units (approximately 140g of alcohol) of alcohol or more per week as measured using Time-Line Follow back for Alcohol Consumption at baseline (day 0);
• Participants will be included if they provide a mobile phone number; and
• Are a veteran of the UK Armed Forces.

Exclusion Criteria:

• Participants will be excluded if they are listed as being 'red' risk by Combat Stress, which is determined by the clinical team following an initial assessment and is based on a traffic light system to assess risk, where red indicates an immediate high risk to the individual and/or others. The application of 'red' risk is applied independently of the research team and is used only where participation in the study could impact clinical treatment. The exclusion will apply only during contact list data extraction.
• Participants will be excluded if they do not have a mobile phone; and
• Participants will be excluded if they have not given Combat Stress consent for contact for research purposes.

To promote open science, consent will be sought from participants to share their data anonymously for research purposes. This data will be released upon completion of the study. Only questionnaire response, remote measurement technology data and alcohol consumption statistics will be shared. All data will be de-identified, and no personal data will be released.

Data is available for access via contact to the lead researcher.

Researchers will be required to sign a Data Sharing Agreement.

Randomisation occurs when a quick response (QR) code is generated and a unique proxy identifier and participant gender is assigned. At this point, participants are automatically randomised to receive the control or intervention arm and are blinded. Block randomisation, of size 2, will be used to ensure equal gender distribution across both conditions. The randomisation procedure is done automatically by the Drinks:Ration platform with no human involvement except to provide a proxy identifier and gender.