Psychobiotics in pediatric autism spectrum disorder: A systematic review of efficacy, mechanisms, and clinical translation

Table 2 Effects of probiotic supplementation on core autism symptoms

Ref.	Study design	Sample size/age	Probiotic intervention	Duration	Outcomes measured	Main findings
Shaaban et al[28]	Prospective open-label study	n = 30; 5-9 years	Lactobacillus acidophilus, Lactobacillus rhamnosus, Bifidobacterium longum (100 × 106 CFU/g)	3 months	ATEC; 6-GSI; stool microbiota	Significant improvement in autism severity and GI symptoms; increased Lactobacillus and Bifidobacterium levels. Probiotic
Narula Khanna et al[25]	Single-blind randomized placebo-controlled trial	n = 180; 2-9 years	Multi-strain probiotic (12 strains; 9 billion CFU per sachet)	3 months	SRS-2; ABC-2; GSI	Significant reductions in behavioral symptoms vs placebo (SRS-2 improvement 47.77% vs 23.33%, P < 0.001); improvements in constipation and diarrhea. Probiotic
Arnold et al[19]	Randomized placebo-controlled crossover pilot trial	n = 13 (10 completed); 3-12 years	VISBIOME probiotic (8 species, mainly Lactobacillus and Bifidobacterium)	8 weeks per treatment phase	Pediatric Quality of Life Inventory (PedsQL-GI); PRAS-ASD; microbiota analysis	Significant improvement in GI complaints vs placebo (P = 0.02); moderate effect size for GI quality of life. Probiotic
Schmitt et al[29]	Randomized controlled phase Ib trial	n = 15 Participants with ASD (18-22 years)	SB-121 investigational probiotic formulation (Lactobacillus reuteri)	4 weeks	Vineland-3 Adaptive Behavior; social preference (eye-tracking)	Significant increase in Vineland-3 Adaptive Behavior Composite score (P = 0.03); treatment was well-tolerated. Probiotic
Sanctuary et al[21]	Randomized double-blind crossover pilot study	n = 8; 2-11 years with ASD and GI symptoms	Bifidobacterium infantis + bovine colostrum product	12 weeks	GI symptoms, immune markers, behavioral symptoms	Treatment was well-tolerated; reductions in some GI symptoms and certain aberrant behaviors were observed. Probiotic
Wang et al[20], 2020	Interventional study (probiotics + prebiotic)	n = 26 children with ASD	Probiotics + fructo-oligosaccharides	30, 60, 108 days	Gut microbiota composition; SCFAs; neurotransmitters; autism severity	Increased beneficial bacteria (Bifidobacterium longum) and reduction in autism and GI symptom severity after intervention. Probiotic
Mazzone et al[32]	Double-blind randomized placebo-controlled pilot trial	n = 43 Children with ASD (21 received probiotic with a mean age of 5.8 ± 1.3 years)	Lactobacillus reuteri combination (strains ATCC-PTA-6475 and DSM-17938)	6 months	Social functioning measures, autism severity, microbiome composition, and immune profile	Probiotic treatment significantly improved social behavior but did not change overall autism severity, repetitive behaviors, microbiome composition, or immune markers
Santocchi et al[33]	Randomized controlled trial protocol	n = 100 preschool children with ASD	Multi-strain probiotic mixture (Vivomixx®)	6 months	GI symptoms, autism severity, cognitive and language development, biomarkers, neurophysiology	Designed to evaluate effects of probiotics on GI symptoms, autism severity, and neurophysiological patterns; results intended to clarify gut-brain axis mechanisms
Santocchi et al[30]	Double-blind randomized placebo-controlled trial	n = 85 preschoolers with ASD (mean age 42 years)	De Simone Formulation (multi-strain probiotic)	6 months	ADOS-CSS, GI symptoms, adaptive functioning, sensory profile	No overall improvement in autism severity; subgroup without GI symptoms showed improvement in ADOS scores, while children with GI symptoms showed improvements in GI symptoms and adaptive functioning.
Kong et al[26]	Randomized double-blind placebo-controlled pilot trial	n = 35 individuals with ASD aged 3-20 years	Lactobacillus plantarum PS128 (6 × 1010 CFU) followed by PS128 + oxytocin combination therapy	28 weeks (oxytocin added at week 16)	SRS, ABC, CGI, microbiome and inflammatory markers	Combination therapy significantly improved SRS and ABC scores and CGI improvement compared with placebo; microbiome network hubs associated with social cognition improved
Li et al[27]	Prospective randomized controlled trial	n = 41 children with ASD	Oral probiotics + ABA therapy vs ABA alone	3 months	ATEC; gut microbiota composition	Both groups improved, but ATEC scores decreased significantly more in the probiotic + ABA group; probiotics increased beneficial bacteria (Bifidobacterium, Lactobacillus) and reduced Shigella and Clostridium
Meguid et al[34]	Interventional clinical study	n = 40 children with ASD aged 2-5 years	Nutritional supplement containing Bifidobacterium spp. and Lactobacillus spp.	3 months	CARS; ADI-R; GI symptom questionnaire; stool microbiota	Significant increases in probiotic bacterial counts with improvement in sleep, anxiety, and clinical symptoms; findings suggest probiotics may reduce ASD severity and correct dysbiosis
Darwesh et al[35]	Observational microbiome study	Children with ASD vs typically developing controls	No intervention (microbiome analysis of Lactobacillus plantarum, Lactobacillus reuteri, Bifidobacterium longum)	Cross-sectional	CARS, SSP, microbiome PCR analysis	Lower abundance of psychobiotic bacteria in ASD children; correlations found between psychobiotic abundance and sensory and behavioral scores
Billeci et al[31]	Randomized double-blind placebo-controlled trial	Preschool children with ASD	Multi-strain probiotic (same formulation as Santocchi trial)	6 months	EEG parameters, clinical measures, and inflammatory markers	Probiotic treatment modified brain electrical activity (reduced beta/gamma power and increased coherence), suggesting normalization of neural connectivity; EEG changes correlated with clinical measures
Liu et al[24]	Randomized double-blind placebo-controlled trial	n = 80 boys aged 7-15 years (71 completed)	Lactobacillus plantarum PS128	4 weeks	ABC-T, SRS, SNAP-IV, CBCL, CGI	PS128 showed improvements in opposition/defiance, hyperactivity, anxiety, and SNAP-IV scores, particularly in younger children; overall behavioral trends improved
Mensi et al[23]	Real-world observational study	n = 131 children and adolescents with ASD	Lactobacillus plantarum PS128 (3 × 1010-6 × 1010 CFU) vs other probiotics	6 months	CGI	77% showed clinical improvement, particularly younger children; PS128 produced greater improvements and fewer side effects compared with other probiotics

ABA: Applied Behavior Analysis; ABC: Aberrant Behavior Checklist; ABC-2: Aberrant Behavior Checklist, second edition; ABC-T: Aberrant Behavior Checklist-total score; ADI-R: Autism diagnostic interview-revised; ADOS-CSS: Autism diagnostic observation schedule-calibrated severity score; ASD: Autism spectrum disorder; ATEC: Autism Treatment Evaluation Checklist; CBCL: Child Behavior Checklist; CARS: Childhood Autism Rating Scale; CFU: Colony-forming units; CGI: Clinical global impression; EEG: Electroencephalogram; GI: Gastrointestinal; GSI: Gastrointestinal severity index; PedsQL-GI: Pediatric Quality of Life Inventory–gastrointestinal module; PRAS-ASD: Pediatric rating of autism severity-autism spectrum disorder; SB-121: Investigational probiotic (synbiotic) formulation SB-121; SCFAs: Short-chain fatty acids; SNAP-IV: Swanson, Nolan, and Pelham Rating Scale–version IV; SRS: Social Responsiveness Scale.