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L-Carnitine

L-carnitine is best known for its role in fat metabolism and energy production.

Evidence · Grade D
Meta-analysis availableSystematic review availableHuman trial evidenceTraditional useInteraction riskNeeds more research

Amino-acid derivative used in hyperthyroidism to blunt thyroid hormone action peripherally.

L-carnitine is a naturally occurring amino acid derivative that plays a crucial role in energy production within the body. It is often supplemented to support various metabolic processes. People commonly take it orally in capsule, tablet, or liquid forms, often alongside meals. Its use is studied for conditions ranging from cardiovascular health to exercise performance.

Quick answer

What it is: L-carnitine is a naturally occurring amino acid derivative that plays a crucial role in energy production within the body.

May support:Multiple Sclerosis (MS), Metabolic Syndrome, Heart Failure, Obesity, Sleep Apnea, High Cholesterol, Non-Alcoholic Fatty Liver Disease (NAFLD), Chronic Fatigue, Hyperthyroidism, Atherosclerosis, Chronic Fatigue Syndrome, Atrial Fibrillation, Graves' Disease, Fibromyalgia

Evidence:Evidence · Grade D

Evidence Summary

Evidence · Grade D

Evidence for L-carnitine includes human clinical trials, some meta-analyses, and preclinical studies. The diversity of research and some positive findings in specific areas contribute to its 'B' grade, suggesting some supportive but not universally conclusive evidence.

Last reviewed · Jun 2026

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Why It Works

L-carnitine appears to facilitate the transport of long-chain fatty acids into the mitochondria, where they can be oxidized for energy. It may also exert antioxidant effects and influence thyroid hormone activity.

How it works in more detail

L-carnitine acts as a carrier molecule, enabling fatty acyl-CoAs to cross the inner mitochondrial membrane, a critical step in beta-oxidation. It may also support mitochondrial function and integrity. Furthermore, preclinical and some clinical studies suggest L-carnitine can inhibit the entry of thyroid hormones (T3 and T4) into the cell nucleus, which could be relevant in conditions of thyroid hormone excess, such as hyperthyroidism.

How to use

Always consult a qualified clinician.

Editorial guidance

Suggested dosage
1000 mg/day L-carnitine in divided doses.
Research dosage range
500–3000 mg/day
Typical onset
Some effects, particularly those related to exercise performance, may appear acutely, while others, like those impacting metabolic parameters, may require several weeks to months of consistent use to become apparent.
Typical forms
capsule, tablet, liquid, powder
Quality markers
When selecting an L-carnitine supplement, look for products that specify the form (e.g., L-carnitine tartrate, acetyl-L-carnitine) as different forms may have different applications. Third-party testing for purity and potency is also a strong indicator of a quality product, ensuring it is free from contaminants.
Medication interactions
  • Thyroid hormone replacement therapy (may increase effects of thyroid hormones)
  • Anticoagulants (e.g., warfarin, may increase bleeding risk)
  • Valproic acid (may reduce L-carnitine levels)
Avoid if
  • Kidney disease (unless under medical supervision)
  • Seizure disorders (may increase seizure frequency)
  • Hypothyroidism (may interfere with thyroid hormone)

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Suggested dosage

1000 mg/day L-carnitine in divided doses.

General guidance — discuss specifics with a clinician.

Active medicinal compounds

L-carnitine, acetyl-L-carnitine.

Traditional use

Identified in muscle in the early 1900s; clinically studied in hyperthyroidism since the 2000s.

Safety

Safety warnings

Can cause GI upset, fishy body odor. Caution in seizure disorders.

Avoid if

  • Kidney disease (unless under medical supervision)
  • Seizure disorders (may increase seizure frequency)
  • Hypothyroidism (may interfere with thyroid hormone)

Medication interactions

  • Thyroid hormone replacement therapy (may increase effects of thyroid hormones)
  • Anticoagulants (e.g., warfarin, may increase bleeding risk)
  • Valproic acid (may reduce L-carnitine levels)

Reported side effects

  • Nausea
  • Vomiting
  • Diarrhea
  • Abdominal cramps
  • Fishy body odor

General guidance — discuss specifics with a clinician.

Evidence ecosystem

Scientific literature, clinical guidance, government sources, ongoing research, traditional use, and lived experience — grouped by source type and quality.

Overall grade (D)

Evidence for L-carnitine includes human clinical trials, some meta-analyses, and preclinical studies. The diversity of research and some positive findings in specific areas contribute to its 'B' grade, suggesting some supportive but not universally conclusive evidence.

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Meta-Analyses(5)

Pooled analyses across multiple human trials.

Very High Quality
  • The Effect of the L-Carnitine Supplementation on Obesity Indices: An Umbrella Meta-Analysis.

    Hamedi-Kalajahi F, Zarezadeh M, Malekahmadi M, Jamilian P, Jamilian P, Molani-Gol R · International journal for vitamin and nutrition research. Internationale Zeitschrift fur Vitamin- und Ernahrungsforschung. Journal international de vitaminologie et de nutrition · 2025 · n=352

    Obesity, one of the most frequent health risks, represents a global public health problem. The potential impact of L-carnitine, a vital nutrient for energy metabolism, on weight loss is worth considering. However, given the inconclusive results from recent meta-analyses on L-carnitine, we conducted an umbrella meta-analysis of placebo-controlled and controlled trials to evaluate the effect of L-carnitine on anthropometric indices. Data synthesis: A comprehensive search approach using the relevant keywords was performed in PubMed, Web of Science, Scopus databases, and Google Scholar up to March 2023. Meta-analyses published in English that provided quantitative statistical analyses regarding the effects of L-carnitine on body weight, waist circumference (WC), and body mass index (BMI) were included. A random-effects model and subgroup analysis were performed based on the L-carnitine dosage and study population. A total of 16,352 participants were included. Intervention durations range

    Meta-AnalysisPubMedVery High Quality
  • Nutraceutical interventions for erectile dysfunction: a systematic review and network meta-analysis.

    Barbonetti A, Tienforti D, Antolini F, Spagnolo L, Cavallo F, Di Pasquale AB · The journal of sexual medicine · 2024 · n=1000

    Although nutraceutical-based treatments are often offered for erectile dysfunction (ED), their efficacy remains doubtful, and the choice of one substance over the other is challenged by the dearth of head-to-head comparative studies. We aimed to compare the efficacy of available nutraceutical interventions, alone or in combination with phosphodiesterase type 5 inhibitors (PDE5i), in improving erectile function in men with ED through a network meta-analysis (NMA), which incorporates direct and indirect evidence into one model thus generating a hierarchy of effectiveness. PubMed, Scopus, Web of Sciences, and Cochrane Library databases were searched for randomized placebo-controlled trials (RCTs) assessing the effect of any nutraceutical regimen in improving erectile function when compared to each other, placebo, and/or PDE5i in men with ED. Data were included in a random-effects NMA, where efficacy of treatments was ranked by surface under the cumulative ranking curve (SUCRA). Two NMAs

    Meta-AnalysisPubMedVery High Quality
  • Safety and efficacy of antioxidant therapy in children and adolescents with attention deficit hyperactivity disorder: A systematic review and network meta-analysis.

    Zhou P, Yu X, Song T, Hou X · PloS one · 2024 · n=650

    To systematically evaluate the safety and efficacy of antioxidant therapy in children and adolescents with attention deficit hyperactivity disorder (ADHD). Randomized controlled trials and prospective studies on antioxidant therapy in children and adolescents with ADHD were searched in PubMed, Embase, and Cochrane Library from the inception of databases to November 12, 2022. Two investigators independently screened the literature, extracted data, and evaluated the quality of the included studies. Network meta-analysis (PROSPERO registration number CRD 42023382824) was carried out by using R Studio 4.2.1. 48 studies involving 12 antioxidant drugs (resveratrol, pycnogenol, omega-3, omega-6, quercetin, phosphatidylserine, almond, vitamin D, zinc, folic acid, ginkgo biloba, Acetyl-L-carnitine) were finally included, with 3,650 patients. Network meta-analysis showed that omega-6 (0.18), vitamin D (0.19), and quercetin (0.24) were the top three safest drugs according to SUCRA. The omega-3

    Meta-AnalysisPubMedVery High Quality

Systematic Reviews(3)

Structured reviews of the full body of evidence (incl. Cochrane).

Very High Quality
  • The pediatric psychopharmacology of autism spectrum disorder: A systematic review - Part II: The future.

    Persico AM, Asta L, Chehbani F, Mirabelli S, Parlatini V, Cortese S · Progress in neuro-psychopharmacology & biological psychiatry · 2025

    Part I of this systematic review summarized the state-of-the-art of pediatric psychopharmacology for Autism Spectrum Disorder (ASD), a severe and lifelong neurodevelopmental disorder. The purpose of this Part II follow-up article is to provide a systematic overview of the experimental psychopharmacology of ASD. To this aim, we have first identified in the Clinicaltrials.gov website all the 157 pharmacological and nutraceutical compounds which have been experimentally tested in children and adolescents with ASD using the randomized placebo-controlled trial (RCT) design. After excluding 24 drugs already presented in Part I, a systematic review spanning each of the remaining 133 compounds was registered on Prospero (ID: CRD42023476555), performed on PubMed (August 8, 2024), and completed with EBSCO, PsycINFO (psychology and psychiatry literature) and the Cochrane Database of Systematic reviews, yielding a total of 115 published RCTs, including 57 trials for 23 pharmacological compounds an

    Systematic ReviewPubMedVery High Quality
  • L-Carnitine in the Treatment of Psychiatric and Neurological Manifestations: A Systematic Review.

    Wang W, Pan D, Liu Q, Chen X, Wang S · Nutrients · 2024

    L-carnitine (LC), a vital nutritional supplement, plays a crucial role in myocardial health and exhibits significant cardioprotective effects. LC, being the principal constituent of clinical-grade supplements, finds extensive application in the recovery and treatment of diverse cardiovascular and cerebrovascular disorders. However, controversies persist regarding the utilization of LC in nervous system diseases, with varying effects observed across numerous mental and neurological disorders. This article primarily aims to gather and analyze database information to comprehensively summarize the therapeutic potential of LC in patients suffering from nervous system diseases while providing valuable references for further research. A comprehensive search was conducted in PubMed, Web Of Science, Embase, Ovid Medline, Cochrane Library and Clinicaltrials.gov databases. The literature pertaining to the impact of LC supplementation on neurological or psychiatric disorders in patients was revie

    Systematic ReviewPubMedVery High Quality
  • Dietary Interventions in the Management of Fibromyalgia: A Systematic Review and Best-Evidence Synthesis.

    Lowry E, Marley J, McVeigh JG, McSorley E, Allsopp P, Kerr D · Nutrients · 2020

    Fibromyalgia syndrome (FMS) is characterised by chronic widespread pain alongside fatigue, poor sleep quality and numerous comorbidities. It is estimated to have a worldwide prevalence of 1.78%, with a predominance in females. Treatment interventions for fibromyalgia have limited success, leading to many patients seeking alternative forms of treatment, including modifications to their diet and lifestyle. The effectiveness of dietary changes in fibromyalgia has not been widely researched or evaluated. This systematic review identified twenty-two studies, including 18 randomised control trials (RCTs) and four cohort studies which were eligible for inclusion. In total these studies investigated 17 different nutritional interventions. Significant improvements in reported pain were observed for those following a vegan diet, as well as with the low fermentable oligo di-mono-saccharides and polyols (FODMAP) diets. Supplementation with Chlorella green algae, coenzyme Q10, acetyl-l-carnitine or

    Systematic ReviewPubMedVery High Quality

Clinical Guidelines(1)

Recommendations from medical societies (NICE, AHA, ADA, ACG, Endocrine Society…).

High Quality
  • Guidelines on management of cyclic vomiting syndrome in adults by the American Neurogastroenterology and Motility Society and the Cyclic Vomiting Syndrome Association.

    Venkatesan T, Levinthal DJ, Tarbell SE, Jaradeh SS, Hasler WL, Issenman RM · Neurogastroenterology and motility · 2019

    The increasing recognition of cyclic vomiting syndrome (CVS) in adults prompted the development of these evidence-based guidelines on the management of CVS in adults, which was sponsored by the American Neurogastroenterology and Motility Society (ANMS) and the Cyclic Vomiting Syndrome Association (CVSA). GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) framework was used and a professional librarian performed the literature search. The expert committee included the President of the CVSA who brought a patient perspective into the deliberations. The committee makes recommendations for the prophylaxis of CVS, treatment of acute attacks, diagnosis, and overall management of CVS. The committee strongly  recommends that adults with moderate-to-severe CVS receive a tricyclic antidepressant (TCA), such as amitriptyline, as a first-line prophylactic medication and receive topiramate or aprepitant as alternate prophylactic medications. Zonisamide or levetiracetam

    Clinical GuidelinePubMed (Practice Guideline)Very High Quality

Randomized Human Trials(2)

Controlled human studies with random assignment.

High Quality
  • Effects of L-Carnitine and Coenzyme Q10 Supplementation on Lower Urinary Tract Symptoms in Men with Benign Prostatic Hyperplasia: A Randomized, Controlled, Clinical Trial.

    Norouzi M, Mahboobi S, Eftekhari MH, Salehipour M, Ghaem H, Mirzakhanlouei A · Nutrition and cancer · 2024

    The prevalence of benign prostatic hyperplasia (BPH) and its associated lower urinary tract symptoms (LUTS) increases with age. Considering that BPH drug treatment is associated with complications, this study aimed to investigate the effects of L-carnitine (LC) and Coenzyme Q10 (CoQ10) supplementation as an adjunct therapy to finasteride in the management of LUTS in older men affected with BPH. Fifty eligible volunteers (25 per group) were randomly assigned to either intervention (finasteride + LC and CoQ10 supplements) or control (finasteride + placebo) groups. International prostate symptom score (IPSS), international index of erectile function (IIEF), quality of life index (QoL), as well as serum levels of Prostate-specific antigen (PSA), were assessed. Prostate ultrasound evaluation was also performed, before and after 8 wk of intervention. Supplementation with LC and CoQ10 led to a significant decrease in prostate volume (p < 0.001) as

    Randomized TrialPubMedHigh Quality
  • Daily oral supplementation with collagen peptides combined with vitamins and other bioactive compounds improves skin elasticity and has a beneficial effect on joint and general wellbeing.

    Czajka A, Kania EM, Genovese L, Corbo A, Merone G, Luci C · Nutrition research (New York, N.Y.) · 2018 · n=120

    Aging is a multifactorial and natural process that causes physiological changes in organs, tissues and cells over time. In the skin and cartilage, aging leads to a decrease in the synthesis and changes in the arrangement of proteoglycans and collagen, in addition to the loss of glycosaminoglycans, which are responsible for the integrity and health of these tissues. We hypothesized that daily oral supplementation with a liquid nutraceutical containing hydrolyzed fish collagen, vitamins, antioxidants and other active ingredients could improve skin texture and elasticity, and in addition have a protective effect on joint health. A double-blind, randomized, placebo-controlled clinical trial was conducted on 120 subjects who consumed either the test product or placebo on a daily basis for 90 days. Subjects consuming the test product had an overall significant increase in skin elasticity (+40%; P < .0001) when compared to placebo. Histological analysis of skin biopsie

    Randomized TrialPubMedHigh Quality

Observational Studies(5)

Cohort, case-control, and cross-sectional human studies.

Moderate Quality
  • Dietary supplements and prevention of preeclampsia.

    Ushida T, Tano S, Matsuo S, Fuma K, Imai K, Kajiyama H · Hypertension research : official journal of the Japanese Society of Hypertension · 2025

    Preeclampsia (PE) is a common pregnancy complication characterized by hypertension, proteinuria, and end-organ dysfunction. However, to date, no effective treatment has been established other than iatrogenic delivery, and the importance of prevention as an alternative approach to addressing PE has been emphasized. There is growing evidence on the effectiveness of pharmacological and non-pharmacological prophylaxis in preventing PE. In this review, we focused on dietary supplements as non-pharmacological prophylaxis for PE. Calcium is a well-documented supplement for the prevention of PE. Daily 500 mg calcium supplementation can roughly halve the risk of PE in settings where calcium intake is low, including in Japan. According to recent systematic reviews and network meta-analyses, current evidence on the efficacy of vitamin D supplementation is inconsistent. Although vitamin D is a candidate for the prevention of PE, future large-scale randomized control trials are necessary to

    Observational StudyPubMedLow Quality
  • Non-drug pain relievers active on non-opioid pain mechanisms.

    Marchesi N, Govoni S, Allegri M · Pain practice : the official journal of World Institute of Pain · 2022

    This review is aimed to summarize the pain-relieving effect of non-drug substances, mostly prescribed as integrators in treatment of pain, including especially in chronic postoperative pain (CPSP) and in chronic back pain after acute episodes. Their use reflects the fact that the current treatments for these syndromes continue to pose problems of unsatisfactory responses in a significant portion of patients and/or of an excess of side effects like those noted in the present opioid crisis. As integrators are frequently introduced into the market without adequate clinical testing, this review is aimed to collect the present scientific evidence either preclinical or clinical for their effectiveness. In particular, we reviewed the data on the use of: B vitamins; vitamin C; vitamin D; alpha lipoic acid (ALA); N-acetylcysteine; acetyl L-carnitine; curcumin; boswellia serrata; magnesium; coenzyme Q10, and palmitoylethanolamide. The combination of preclinical findings and clinical observations

    Observational StudyPubMedLow Quality
  • Nutraceuticals in Patients With Heart Failure: A Systematic Review.

    Hopper I, Connell C, Briffa T, De Pasquale CG, Driscoll A, Kistler PM · Journal of cardiac failure · 2020 · n=50

    Nutraceuticals are pharmacologically active substances extracted from vegetable or animal food and administered to produce health benefits. We recently reviewed the current evidence for nutraceuticals in patients diagnosed with heart failure as part of the writing of the Australian Guidelines for the prevention, diagnosis, and management of heart failure. A systematic search for studies that compared nutraceuticals to standard care in adult patients with heart failure was performed. Studies were included if >50 patients were enrolled, with ≥6 months follow-up. If no studies met criteria then studies <50 patients and <6 months follow-up were included. The primary outcomes included mortality/survival, hospitalization, quality of life, and/or exercise tolerance. Iron was not included in this review as its role in heart failure is already well established. Forty studies met the inclusion criteria. The strongest evidence came from studies of polyunsaturated fatty acids, wh

    Observational StudyPubMedLow Quality

Clinical Trial Registries(8)

Registered ongoing or completed trials (ClinicalTrials.gov).

Moderate Quality

Limitations: Existing research often involves small sample sizes and heterogeneity in study designs and populations. More robust, large-scale, placebo-controlled trials are often needed to confirm preliminary findings and establish optimal dosages for various applications.

This page is educational. Statements use phrases like "may support" and "has been studied for"because no remedy here is approved to cure, treat, or reverse any condition. Discussion happens on the ailment pages — community statistics here are derived from those reports. Always consult a qualified clinician.

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