Effect of multispecies probiotics on autism symptoms: protocol for a randomized controlled trial (PROBAUT).

The trial will enroll 110 children aged 7 to 15 years diagnosed with ASD, randomized in a 1:1 ratio to probiotic or placebo for 12 weeks.

• Sample size is 110 children aged 7 to 15 years
• Randomization ratio is 1:1 (probiotic vs. placebo)
• Duration of intervention is 12 weeks
• Study design is randomized, double-blind, placebo-controlled

The probiotic mixture contains 5 × 10⁹ colony-forming units per dose comprising eight bacterial strains.

• Dose is 5 × 10⁹ colony-forming units per dose
• Strains included: Bacillus subtilis W20, Bifidobacterium infantis W17, Bifidobacterium lactis W51, Lactobacillus acidophilus W37, Levilactobacillus brevis W63, Lacticaseibacillus rhamnosus W140, Lactococcus lactis W19, and Propionibacterium freudenreichii W200
• This is a multispecies formulation spanning multiple bacterial genera

The primary outcome measure is the severity of core autism symptoms assessed using the Autism Symptom Rating Scales (ASRS).

• ASRS will be used to assess core autism symptoms
• Assessments will be conducted twice: at baseline and after 12 weeks of intervention
• The primary outcome focuses specifically on core autism symptoms

Secondary outcomes include quality of life, sleep impairments, parental stress levels, gastrointestinal symptoms, and urinary p-cresol levels.

• Five secondary outcome domains are specified: quality of life, sleep impairments, parental stress levels, gastrointestinal symptoms, and urinary p-cresol levels
• All secondary outcomes will be assessed at baseline and after 12 weeks of intervention
• Urinary p-cresol is included as a biomarker outcome, reflecting gut microbiota metabolic activity

The trial has received ethics approval and is registered on ClinicalTrials.gov.

• Ethics approval was granted by the Ethics Committee of the Medical University of Warsaw
• ClinicalTrials.gov identifier is NCT06448767
• Trial was registered on 3 June 2024
• Protocol version is Version 2, dated 27 October 2025