L-carnosine for autistic children: an early promise the later trials did not confirm

Sample size: Systematic review of 20 antioxidant trials; the L-carnosine randomised trials within it enrolled 43, 63 and 70 children, with a further 2024 pilot trial
Demographics: Autistic children roughly aged 3-12, across trials in Iran, India and elsewhere; most trials ran 8 to 10 weeks
Key outcome: No trial showed a reliable improvement in core autism symptoms. The largest (70 children, 800 mg/day added to risperidone for 10 weeks) missed its primary target of irritability entirely, improving only hyperactivity/non-compliance. The review concludes there is no solid evidence of clinical efficacy for carnosine.
Methodology: A PROSPERO-registered systematic review searched PubMed, Scopus, ClinicalTrials.gov and Cochrane-Ovid, included 20 antioxidant trials in autism and assessed them with the Cochrane Risk-of-Bias tool. Its L-carnosine findings are read here alongside the underlying randomised, double-blind, placebo-controlled trials and a 2024 pilot trial that also measured carnosine levels in blood.
Researchers: D. A. Abraham, Z. Mehrazad-Saber, S. Kheirouri, R. Hajizadeh-Zaker, S. Akhondzadeh, M. G. Rajanandh
Institutes: Journal of Autism and Developmental Disorders (PROSPERO CRD42023490581), Tehran University of Medical Sciences, Roozbeh Hospital, SRM College of Pharmacy, India (CTRI/2019/07/020102)

Limitations:

• Trials are small — 43 to 70 children — and short, typically 8 to 10 weeks
• Doses varied widely (500 mg/day, 800 mg/day, 10-15 mg/kg), so the trials are not directly comparable and a dose effect cannot be ruled out
• The review judged the antioxidant trials overall to carry a high risk of bias
• The scattered positive findings are single subscales in single trials, unreplicated — the pattern you would also expect from chance
• Including very young children risks mistaking normal developmental progress for a treatment effect

• The 2025 systematic review classed L-carnosine as showing improvement in social cognition and communication in its qualitative synthesis, but concluded in the same paper that carnosine 'has no solid evidence of its clinical efficacy across the included trials'.
• In a 70-child randomised double-blind trial, carnosine 800 mg/day added to risperidone for 10 weeks produced no significant benefit on irritability — the primary outcome — nor on lethargy, stereotypic behaviour or inappropriate speech; only hyperactivity/non-compliance improved more than placebo.
• In a 43-child trial at 500 mg/day, carnosine did not change autism severity on the GARS-2, but did significantly reduce daytime sleepiness, parasomnias and total sleep disorder scores.
• In a 63-child trial (32 carnosine, 31 placebo), there was no statistically significant improvement on the CARS2-ST autism rating or the BEARS sleep screen, apart from the single 'intellectual response' item.
• A 2024 pilot trial confirmed carnosine does reach the bloodstream after supplementation, yet found no significant difference on any outcome measure and concluded it was ineffective for managing autism in children.
• A possible reason: a separate trial found carnosine did not shift the oxidative-stress markers it is supposed to act on, suggesting the proposed mechanism may not translate into neurological change.

• If you are considering carnosine for core autism symptoms — social communication or repetitive behaviour — the controlled evidence does not support that expectation.
• The one finding that recurs in a recognisable form is sleep. If sleep is your main concern, that is worth raising with your paediatrician, who can also check the more established causes first.
• Carnosine was generally well tolerated in these trials, so the main costs are financial and practical rather than medical — but 'safe' is not the same as 'works'.
• Nothing here suggests replacing therapy or prescribed medication with a supplement; the review is explicit that antioxidants are not justified as a standalone treatment.
• Tell your child's doctor about any supplement you start, including over-the-counter ones, so it can be tracked alongside everything else.

• Marketing for carnosine often leans on an early 2002 trial that reported language and behaviour gains. The larger, better-controlled trials that followed have not reproduced that result, which is the more reliable signal.
• Absence of proof is not proof of absence: these trials are small and short, and a modest benefit in some subgroup of children could still be missed.
• Doses differed several-fold between trials, and none established what an effective dose would even be.
• The positive results that do appear are isolated subscales in single studies. Treat any one of them as a hypothesis, not a finding.
• Supplements are regulated far more loosely than medicines, so what is on the label may not match what is in the bottle.

• Efficacy of Antioxidant-Based Pharmacological Therapies in Autism Spectrum Disorder: A Systematic Review — Journal of Autism and Developmental Disorders, 2025, doi:10.1007/s10803-025-07059-5
• l-Carnosine as an Adjunctive Therapy to Risperidone in Children with Autistic Disorder: A Randomized, Double-Blind, Placebo-Controlled Trial — Hajizadeh-Zaker et al., 2017, Journal of Child and Adolescent Psychopharmacology 28(1):74-81
• Effect of l-Carnosine as adjunctive therapy in the management of children with autism spectrum disorder: a randomized controlled study — Ann Abraham et al., 2020, Amino Acids 52(11-12):1521-1528
• Estimation of Plasma Concentration of L-Carnosine and its Correlation with Core Symptoms of Autism Spectrum Disorder Children: A Pilot Clinical Trial — Frontiers in Bioscience-Landmark, 2024, 29(10):365 (CTRI/2019/07/020102)
• Effect of L-carnosine in children with autism spectrum disorders: a systematic review and meta-analysis of randomised controlled trials — Abraham, Undela, Narasimhan & Rajanandh, 2021, Amino Acids 53(4):575-585

• What risperidone 0.5 mg (sold as Sizodone) does — and does not do — for autistic children — Behaviour
• Understanding Sensory Issues and Humming in Autistic Children: What Caregivers Need to Know — Sensory
• Echolalia in Autism: What the Research Tells Us About Why Children Repeat Words and Phrases — Communication

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This summary was prepared by the Curioler research agent. It is not medical advice. Always consult a qualified professional before making decisions about your child's care.