What is the beneficial dose of L-Carnitine (L-Carnitine) for Autism Spectrum Disorder (ASD)?

L-Carnitine Dosage for Autism Spectrum Disorder

The recommended beneficial dose of L-Carnitine for Autism Spectrum Disorder (ASD) is 50 mg/kg bodyweight/day, which has been shown to significantly improve clinical measurements of ASD severity in a randomized controlled trial. 1

Evidence for L-Carnitine in ASD

L-Carnitine plays several important roles in the central nervous system and mitochondrial metabolism. A subgroup of patients with ASD (less than 20%) appears to have L-carnitine metabolism disorders, and for these patients, dietary supplementation with L-carnitine may be beneficial. 2

The strongest evidence comes from a prospective double-blind, randomized clinical trial that used a standardized regimen of 50 mg L-carnitine/kg bodyweight/day for 3 months. This study demonstrated:

• Significant improvements in Childhood Autism Rating Scale (CARS) scores
• Improved Clinical Global Impression (CGI) scores
• Better Autism Treatment Evaluation Checklist (ATEC) scores
• Positive correlations between changes in serum free-carnitine levels and clinical improvements 1

Dosing Considerations

• Standard effective dose: 50 mg/kg bodyweight/day 1
• Safety profile:
  • Doses of 50-100 mg/kg/day are generally well tolerated 3
  • Higher doses (≥3g/day or 200 mg/kg/day) may cause side effects including:
    • Gastrointestinal symptoms
    • "Fishy" body odor
    • Nausea and vomiting
    • Abdominal cramps
    • Diarrhea 4, 3

Monitoring and Administration

• Baseline assessment of carnitine status may be helpful before initiating therapy
• Carnitine deficiency is confirmed by:
  • Acyl:free carnitine ratio greater than 0.4, or
  • Total serum carnitine value less than 40 μmol/L 4
• Treatment duration of at least 3 months is recommended to evaluate efficacy 1
• Monitor for clinical response using standardized assessment tools (CARS, CGI, ATEC)

Limitations and Considerations

• Not all children with ASD will benefit from L-carnitine supplementation
• The subgroup most likely to benefit are those with documented carnitine deficiency or abnormal carnitine metabolism 2
• Current guidelines do not specifically recommend L-carnitine for ASD, as the evidence base is still developing
• More research is needed to identify specific biomarkers that could predict response to L-carnitine therapy

Cautions

• Patients on thyroid medication should have thyroid function tests monitored if starting L-carnitine 5
• L-carnitine should be administered at different times than levothyroxine to avoid potential interference with absorption 5
• Patients should be monitored for potential side effects, particularly at higher doses

While the evidence for L-carnitine in ASD is promising, particularly at the 50 mg/kg/day dose, larger clinical trials are still needed to fully establish its efficacy and identify the specific subgroups of ASD patients who would benefit most from this intervention.