Probiotic Study in Alcohol Recovery

Recruitment rate will be calculated as the number of participants enrolled divided by the total number of participants assessed for eligibility, expressed as a percentage.

Retention rate will be calculated as the number of participants completing the 4-week intervention divided by the total number enrolled, expressed as a percentage, and will be reported overall and by study arm.

Adherence will be calculated as the number of capsules consumed relative to the 28 capsules prescribed across the 4-week intervention period, based on participant-reported capsule counts, and expressed as a percentage of the total prescribed dose.

Acceptability of the intervention will be assessed via verbal feedback requested from the participants at the end of the 4-week intervention period, covering participants' experience of intervention components including capsule-taking and stool sample collection procedures.

Mental health symptoms will be assessed using the Depression Anxiety Stress Scales-12 (DASS-12), a 12-item self-report questionnaire measuring symptoms of depression, anxiety, and stress. Each item is rated on a 4-point Likert scale (0-3), yielding a total score ranging from 0 to 36. Performance will be measured as the total DASS-12 score (range 0-36), with higher scores indicating greater psychological distress.

Response inhibition will be assessed using a computerized Go/No-Go task. Participants are required to respond to "go" stimuli and withhold responses to "no-go" stimuli. Performance will be measured as the number of commission errors (responses during no-go trials; count) and the number of correct responses (correct responses to go trials; count), with higher commission errors indicating poorer response inhibition and higher correct responses indicating better task performance.

Alcohol craving will be assessed using the Penn Alcohol Craving Scale (PACS), a 5-item self-report questionnaire measuring frequency, intensity, and duration of alcohol cravings over the past week. Each item is rated on a scale from 0 to 6, yielding a total score ranging from 0 to 30. Performance will be measured as the total PACS score (range 0-30), with higher scores indicating greater alcohol craving severity.

Gut health will be assessed using 16S ribosomal RNA (rRNA) gene sequencing of stool samples collected and analysed in the laboratory. Microbial composition will be characterised using standard bioinformatics pipelines. Outcomes will include alpha diversity (within-sample diversity; e.g., Shannon diversity index) and beta diversity (between-sample differences in microbial composition). Performance will be measured as diversity indices (unitless values) and distance metrics for beta diversity, with higher alpha diversity generally indicating greater microbial diversity and gut health.

Working memory will be assessed using a computerized N-back task (1-back, 2-back, 3-back conditions). Participants respond when a stimulus matches one presented previously (1-3 trials earlier). The task includes 50 trials per condition with 10 target stimuli. Each stimulus is presented for 1000 ms. Performance will be measured based on the number of commission errors (count) and number of correct responses (count), with higher correct responses indicating better working memory performance and higher commission errors indicating poorer performance.

Drinking behaviour will be assessed using the Loughborough Alcohol Drinking Questionnaire (LoAD-Q), a 33-item self-report questionnaire measuring three dimensions: emotional drinking, external drinking, and restrained drinking. Each item is rated on a 5-point Likert scale (1 = never to 5 = very often). Subscale scores are calculated by summing item responses within each dimension.

The emotional drinking subscale (13 items) has a score range of 13 to 65, the external drinking subscale (10 items) ranges from 10 to 50, and the restrained drinking subscale (10 items) ranges from 10 to 50. Performance will be measured as subscale total scores, with higher scores indicating greater levels of emotional, external, and restrained drinking behaviour, respectively.

Attention will be assessed using a computerized visual search task in which participants identify target stimuli among distractors. Performance will be measured as reaction time (milliseconds) and accuracy (percentage of correct responses, %) across trials, with lower reaction times indicating better attentional performance and higher accuracy indicating better task performance.

Cognitive bias will be assessed using the Rough Estimation Task (REsT), where participants read a list of alcohol-related, semantically related, and unrelated words and estimate the proportion of alcohol-related words. Performance will be measured as the percentage (%) of words estimated as alcohol-related, with overestimation (>33%) indicating cognitive bias.

Inflammation will be assessed using salivary interleukin-6 (IL-6) measured via enzyme-linked immunosorbent assay (ELISA) using commercially available kits according to manufacturer protocols. Performance will be measured as IL-6 concentration in picograms per millilitre (pg/mL), with higher values indicating greater systemic inflammation.

Disordered eating behaviours will be assessed using the Eating Disorder Examination Questionnaire Short Form (EDE-QS), a 12-item self-report questionnaire measuring eating disorder psychopathology over the past 7 days. Each item is rated on a 4-point scale (0-3), yielding a total score ranging from 0 to 36. Performance will be measured as the total EDE-QS score (range 0-36), with higher scores indicating greater severity of disordered eating behaviours.

Physiological stress will be assessed using salivary cortisol measured via enzyme-linked immunosorbent assay (ELISA) using commercially available kits according to manufacturer protocols. Performance will be measured as cortisol concentration in nanomoles per litre (nmol/L), with higher values indicating greater physiological stress.