L-carnitine: research, side effects and dosage in studies

In short

L-carnitine is a compound the body makes itself that carries fatty acids into the cells' mitochondria, and it is not a peptide [1]regulator. In meta-analyses it lowered weight by about a kilogram more than the comparison on average [7, 8]A, but in large trials it did not relieve fatigue in people with cancer and did not reduce the combined number of deaths and heart failure after a heart attack [12, 21]A. In Finland it has no authorised medicinal product [28]regulator.

• L-carnitine is not a peptide. The body makes it mainly in the liver and kidneys from the amino acids lysine and methionine [1]regulator, and it comes from meat and dairy products in the diet [3].
• The best human evidence concerns weight: in a meta-analysis of 43 randomised trials, weight fell by 1.1 kg more than in the comparison groups on average, but body fat percentage and waist circumference did not change [8]A.
• Several large trials found no benefit: fatigue did not ease more than with placebo in a trial of 376 people with cancer [21]A, and in a trial of 2,330 heart attack patients the combined number of deaths and heart failure over six months did not fall [12]A.
• Side effects are usually stomach complaints and body odour [5]official. L-carnitine raised blood TMAO in humans [25]B [26]B, and in mice TMAO formation was linked to hardening of the arteries [24]C.
• Levocarnitine is on Fimea's medicines list [29]regulator, but it has no marketing authorisation in Finland [28]regulator. The WADA list does not name it, but intravenous infusions of more than 100 ml in 12 hours are banned for athletes [32]regulator.

What is L-carnitine?

L-carnitine, or levocarnitine, is not a peptide, meaning it is not a chain built from amino acids (what a peptide is). EFSA describes carnitine as a quaternary ammonium salt that the body makes mainly in the liver and kidneys from the amino acids lysine and methionine [1]regulator. According to the US prescribing information, its chemical formula is C7H15NO3 [5]official.

In cells, carnitine is needed so that fatty acids can pass from the cytosol into the mitochondria, where energy is made from them [1]regulator. The body's carnitine pool is kept up in three ways: carnitine absorbed from food, the body's own production, and the kidneys taking back almost all filtered carnitine [2]. In food, carnitine is found in meat and dairy products [3].

The most common form in food supplements is L-carnitine [1]regulator. Studies have also used L-carnitine L-tartrate [13]A and a combination of L-carnitine and acetyl-L-carnitine [17, 18]A.

Like NAD+ and NMN, L-carnitine is on this site even though it is not a peptide: NAD+, NMN. All substances: Peptides A-Z.

Evidence at a glance

Each cell gives the kind of study and its source. The letter is the evidence level, not the result.

"-" = no such study is known.

What is L-carnitine used and studied for?

As a medicine, levocarnitine is used for carnitine deficiency. In the US prescribing information the indications are primary carnitine deficiency and secondary deficiency caused by inherited metabolic disorders [5]official, and for the product given into a vein also carnitine deficiency in dialysis patients [6]official. In Finland levocarnitine has no authorised product [28]regulator.

In primary carnitine deficiency, a gene defect in the OCTN2 transporter (SLC22A5) impairs carnitine transport [3]. In a literature review of 621 confirmed patients, the most common symptoms were heart symptoms, mostly cardiomyopathy (23.8%), and symptoms usually began in early childhood [4].

As a supplement and add-on treatment, L-carnitine has been studied in areas including these:

• Weight: several meta-analyses of randomised trials [7, 8]A.
• Type 2 diabetes: blood sugar and blood lipids [9]A.
• Heart attack: mortality and enlargement of the heart after the attack [10, 11, 12]A.
• Exercise: performance and muscle soreness [13, 15]A [14].
• Male fertility: sperm motility [17, 18, 19, 20]A.
• Fatigue in cancer [21, 22]A and dialysis patients [23]A.

Claims online. According to a risk assessment, L-carnitine is popular in weight loss and sports nutrition products [27]. EFSA, however, concluded that a cause and effect relationship has not been established between L-carnitine and faster recovery, endurance capacity, normal LDL cholesterol or sperm production [1]regulator.

How does L-carnitine work?

L-carnitine carries long-chain fatty acids into the mitochondria, where they are broken down for energy (beta-oxidation) [1]regulator [2]. Skeletal and heart muscle use fatty acids as their main energy source [5]official.

That carnitine is needed for burning fat does not mean that extra carnitine increases fat burning. In healthy men, L-carnitine taken with a carbohydrate drink raised muscle carnitine by 21% over 24 weeks, while it did not change in those who took carbohydrate alone. The carbohydrate was there to raise insulin, because the researchers' earlier work showed that insulin increases carnitine uptake into muscle [13]A.

Only part of L-carnitine taken by mouth is absorbed [2], and gut bacteria turn it into trimethylamine (TMA), from which TMAO is formed. People eating a mixed diet made more TMAO from L-carnitine than vegans or vegetarians, and the difference depended on gut bacteria [24]B. TMAO is covered in more detail under side effects.

Has L-carnitine been studied in humans?

Yes, extensively. Randomised trials have been pooled in meta-analyses on weight, diabetes, heart attack, muscle soreness, male fertility, cancer fatigue and dialysis [7, 8, 9, 10, 15, 19, 20, 22, 23]A. The quality and results of the trials vary, however [9, 20]A. The most important ones by topic are below.

Weight

• Meta-analysis (2016). In nine randomised trials (911 adults), people who took L-carnitine lost 1.33 kg more than the comparison group on average. The effect became smaller the longer the supplement was used [7]A.
• Meta-analysis (2020). Across 43 randomised trials, weight fell by 1.13 kg, body mass index by 0.36 units and fat mass by 1.16 kg on average. Body fat percentage and waist circumference did not change. The effect was seen only in people with overweight or obesity, and in dialysis patients body measures did not change [8]A.

Type 2 diabetes

In a meta-analysis of 21 randomised trials (2,041 patients), every gram of L-carnitine a day was linked to a small fall in glycated haemoglobin (HbA1c, -0.16 percentage points), LDL cholesterol (-0.11 mmol/l) and body mass index. Results varied widely between trials, and the authors say they should be interpreted very cautiously [9]A.

Heart attack

• Meta-analysis (2013). In 13 controlled trials (3,629 patients), L-carnitine was linked to 27% lower mortality, 65% fewer ventricular arrhythmias and 40% less chest pain than placebo or control. It did not reduce heart failure or repeat heart attacks [10]A.
• CEDIM (1995). 472 patients with a first anterior heart attack received placebo or L-carnitine, first into a vein and then by mouth for a year. In the L-carnitine group, enlargement of the left ventricle was smaller, but ejection fraction did not differ between the groups [11]A.
• CEDIM 2 (2006). The trial was meant to enrol 4,000 patients but was stopped after 2,330 because enrolment was slow. The combined number of deaths and heart failure over six months did not differ from placebo (9.2% vs 10.5%). Mortality at five days was lower, but that was a secondary endpoint [12]A.

Exercise and muscles

• Muscle carnitine (2011). 14 healthy young men took carbohydrate alone or L-carnitine L-tartrate with carbohydrate for 24 weeks. In the carnitine group, muscle carnitine rose by 21%, 55% less muscle glycogen was used during light exercise, and work output in a performance test rose by 11% from baseline. Work output did not change in the comparison group [13]A.
• Systematic review (2021). Across 11 studies, L-carnitine improved high-intensity performance in some studies but did not affect moderate-intensity performance [14].
• Muscle soreness (2020). In a meta-analysis of seven randomised trials, muscle soreness after exercise eased, and muscle damage markers (CK, myoglobin, LDH) were lower at 24 hours but not after that. The effect was seen only in resistance training and in untrained people [15]A.
• Long-term use (2020). In a review of 11 studies, 24 weeks of L-carnitine did not increase muscle strength in healthy older women [16].

Male fertility

• Lenzi (2004). In 60 infertile men, a combination of L-carnitine and acetyl-L-carnitine for six months improved sperm motility, most in those who had the fewest motile sperm at the start [17]A.
• Sigman (2006). In 21 men, the same combination for 24 weeks did not improve sperm motility compared with placebo [18]A.
• Meta-analyses. In an analysis of seven studies (621 men), L-carnitine or its combination with acetyl-L-carnitine improved sperm motility and shape [19]A. In a broader meta-analysis of 50 trials, carnitine improved motility, but no supplement increased pregnancies or live births, and the certainty of the evidence was low or very low [20]A.

Fatigue in cancer

In a phase III trial, 376 people with cancer took L-carnitine or placebo for four weeks. Blood carnitine rose, but fatigue eased equally in both groups, and there was no difference in depression or pain. There was no benefit in those who had carnitine deficiency at the start either [21]A. A meta-analysis of three studies rated as good quality found no effect on cancer-related fatigue [22]A.

Dialysis patients

A Cochrane review included 52 randomised trials (3,398 patients). L-carnitine may raise haemoglobin slightly (by 0.46 g/dl on average), but it probably has little or no effect on quality of life, fatigue, muscle cramps or the fall in blood pressure during dialysis. According to the authors, the current evidence does not support carnitine supplements for treating dialysis-related deficiency, and the certainty of the evidence is low [23]A.

Who studies L-carnitine?

The meta-analyses on weight, diabetes and muscle soreness used on this page were done mainly at Tehran University of Medical Sciences, and the same author (Shab-Bidar) is on three of them [7, 9, 15]A. The heart attack trials CEDIM and CEDIM 2 were multicentre trials whose authors worked in Italy [11, 12]A. The cancer fatigue trial was run by the cancer research group ECOG (Eastern Cooperative Oncology Group) [21]A.

According to the publication, the authors of the carnitine risk assessment worked at the Council for Responsible Nutrition [27]. The authors of the Cochrane review on dialysis declared their interests in the review [23]A.

Author of this page: editorial team

This page was written by the Molecular Recovery editorial team. The draft was produced with the help of AI, and the claims were checked against the sources (AI policy). The page has not been medically reviewed. How we work: About us.

How long does L-carnitine stay in the body?

L-carnitine leaves the body mainly in the urine (pharmacokinetics). Normally the kidneys take back 98-99% of the filtered carnitine, but when blood levels rise after an extra dose, more carnitine starts to pass into the urine [2].

• Absorption. Of oral doses of 1-6 grams, only 5-18% is absorbed, whereas up to 75% of the smaller amounts in food may be absorbed [2].
• Single dose. In healthy volunteers, a 1.5 gram dose raised the peak blood level by 43% from baseline, and clearance from the body increased fivefold. About 90% of the dose was turned into TMAO [26]B.
• Half-life. In 12 healthy adults, a single 2 gram dose by mouth brought the blood level to its peak in about 3.4 hours, and the half-life was about 60 minutes [34]B.
• Distribution. L-carnitine does not bind to blood proteins. The slowest-equilibrating pool is in skeletal and heart muscle [2].
• Dialysis. Dialysis patients lose carnitine during dialysis, which can lead to deficiency [2].

What are the side effects of L-carnitine?

The most common side effects are stomach complaints. According to the US prescribing information, transient nausea, vomiting, abdominal cramps and diarrhoea have been reported with long-term use, and large doses can cause diarrhoea [5]official.

What the prescribing information and studies found

• Body odour. The prescribing information mentions drug-related body odour, which often lessens when the dose is reduced [5]official.
• Seizures. Seizures have been reported with levocarnitine given by mouth and into a vein, also in patients with no earlier seizures. In those who already had seizures, they have become more frequent or more severe [5]official.
• Hypersensitivity. Taken by mouth, rash, hives and facial swelling have been reported. Given into a vein, serious hypersensitivity reactions such as anaphylaxis have been reported, mostly in dialysis patients [5, 6]official.
• Dialysis trials. In pooled data from 12 trials (1,041 patients), there were no more adverse events in the L-carnitine groups than in the comparison groups [23]A.
• Risk assessment. A 2006 risk assessment judged the evidence of safety to be strong for long-term intake up to 2,000 mg a day. According to the authors, the data on higher amounts were not enough for a confident conclusion [27].

TMAO: what is known

• In mice (animal study). Long-term dietary L-carnitine changed the gut bacteria of mice, increased TMA and TMAO formation and increased hardening of the arteries. This did not happen when the gut bacteria were suppressed at the same time [24]C.
• Association seen in humans. In 2,595 patients undergoing cardiac evaluation, high blood L-carnitine predicted cardiovascular disease only when TMAO was also high [24]B. This is an observed association, not proof of cause and effect.
• With supplement use. In healthy older women, 24 weeks of L-carnitine raised blood TMAO tenfold, but inflammation markers, arterial markers and blood lipids did not change [25]B. In a single-dose study, blood TMAO rose to levels that have earlier been linked to adverse health outcomes [26]B.

When use is stopped

In a follow-up of older women, blood TMAO returned to a normal level within four months after 24 weeks of L-carnitine use was stopped, and stayed there for the next eight months. Blood lipids and white blood cells did not change during follow-up [35]B.

What has not been studied

It is not known whether the rise in TMAO from long-term supplement use affects the heart and blood vessels. According to a review, this needs to be studied in long follow-up studies [16]. More: Side effects and safety.

Interactions and who lacks data

The US prescribing information names one interaction: INR, a measure of blood clotting, has risen in people taking warfarin, and according to the prescribing information INR is monitored when levocarnitine is started or the dose is changed [5]official.

• Pregnancy. There are no adequate, well-controlled studies in pregnant women [5]official.
• Breastfeeding. Levocarnitine has not been specifically studied in breastfeeding mothers [5]official.
• Seizure tendency. Seizures have also been reported in patients who had seizures before [5]official.
• Dialysis patients. Serious hypersensitivity reactions to levocarnitine given into a vein have been reported mostly in them [6]official.

Evidence against and what is not known

Several large or carefully conducted trials found no benefit from L-carnitine [12, 21]A [22]A [23]A.

Counter-evidence

• In CEDIM 2 (2006, 2,330 patients), the combined number of deaths and heart failure did not differ from placebo [12]A; a 2013 meta-analysis reported lower mortality [10]A.
• Fatigue did not ease more than with placebo in a trial of 376 people with cancer [21]A, nor in a meta-analysis of good-quality studies [22]A.
• Sperm motility did not improve in a trial of 21 men [18]A, and no effect of supplements on pregnancies was found [20]A.
• Weight loss was about a kilogram, and body fat percentage and waist did not change [8]A. The effect became smaller as use continued [7]A.
• L-carnitine did not affect moderate-intensity exercise performance [14].
• According to the Cochrane review of dialysis patients, the evidence does not support carnitine supplements for treating dialysis-related deficiency [23]A.

What the evidence does not support

• "L-carnitine is a peptide": it is not. It is an ammonium compound that the body makes from amino acids [1]regulator.
• "L-carnitine burns fat and makes you lose weight": the average difference was about a kilogram, and body fat percentage did not change [8]A.
• "L-carnitine improves endurance and speeds up recovery": according to EFSA, a cause and effect relationship has not been established [1]regulator, although muscle soreness eased in a meta-analysis [15]A.
• "L-carnitine is proven to harm the heart because of TMAO": hardening of the arteries increased in mice [24]C, but in humans arterial markers did not change over 24 weeks of use [25]B.

It is not known whether the small effect on weight lasts with long-term use [7]A, or what a long-term rise in TMAO means for heart health [16].

L-carnitine dosage in studies

In Finland L-carnitine has no approved dosage, because it has no authorised medicinal product here [28]regulator. Below are the amounts used in human studies. They are not recommendations.

What the figures do not tell you. Only 5-18% of oral gram doses is absorbed [2], and in some studies L-carnitine was taken with acetyl-L-carnitine or carbohydrate [13, 17, 18]A. The dose into a vein in the CEDIM trial was given in hospital during treatment of a heart attack [11]A. Human doses with sources: L-carnitine doses in studies. The calculator page explains why it has no L-carnitine preset: L-carnitine and the calculator. On reading study doses: dosing in studies.

L-carnitine vs acetyl-L-carnitine: what is the difference?

Acetyl-L-carnitine is a form of carnitine marketed as a supplement for neurological support [26]B. In a single-dose study it raised blood carnitine much less than L-carnitine: the increase in the area under the concentration curve was 7.7 times smaller. It left the body mostly as carnitine, and both forms produced a lot of TMAO [26]B.

Fertility studies often used a combination of the two, so the share of L-carnitine alone in the results cannot be separated [17, 18, 19]A.

L-carnitine combinations

In several trials L-carnitine was given together with other substances. In the fertility trials its own effect cannot be separated [17, 18]A; in the muscle study the control group took carbohydrate alone, so the result concerns adding carnitine to carbohydrate [13]A.

• Acetyl-L-carnitine. Fertility trials used a combination of L-carnitine and acetyl-L-carnitine, and the results were conflicting [17, 18]A.
• Carbohydrate. Muscle carnitine rose when L-carnitine was taken with a carbohydrate drink for 24 weeks [13]A.
• Leucine. 37 older women did 24 weeks of resistance training. The combination of L-carnitine L-tartrate and leucine did not increase muscle strength or muscle size more than leucine alone or training alone, but blood TMAO rose only in the combination group [36]B.
• Combination product during weight loss medication. A registered, ongoing trial is testing whether a product containing essential amino acids, carnitine, arginine and minerals preserves muscle mass in people losing weight on GLP-1 medicines. The trial is still recruiting [38]E, not peer-reviewed.

Status in the United States

In the United States, levocarnitine is available as a medicine in tablets, oral solution and an injection for use into a vein under the name Carnitor (levocarnitine) [5, 6]official.

• Tablets and oral solution: primary systemic carnitine deficiency and secondary deficiency caused by inherited metabolic disorders [5]official.
• Injection: secondary deficiency caused by inherited metabolic disorders, and prevention and treatment of carnitine deficiency in dialysis patients with end-stage kidney disease [6]official.
• Contraindications: none known according to the prescribing information [5]official.

Is L-carnitine legal in Finland?

The status of L-carnitine depends on the product. Levocarnitine is on Fimea's medicines list, but according to the list not every product containing a listed substance is necessarily a medicine [29]regulator. The site's legal page covers medicines: Peptides and the law in Finland.

• Medicines list. "Levokarnitiini" is in annex 1 of Fimea decision 230/2025, which lists the substances in medicinal use in Finland. Substances in annex 1 are controlled as medicines under section 3 of the Medicines Act. According to the decision, a listed substance may fall under other legislation, an individual product is assessed on things such as its presentation, composition and use, and Fimea decides when needed whether a product is a medicine [29]regulator.
• Marketing authorisation. In EMA's Article 57 data (9 Oct 2026) there are levocarnitine products in 12 EU countries and Northern Ireland, but not in Finland, and there is no central EU-wide authorisation [28]regulator.
• Food supplement. According to EFSA, L-carnitine is the form commonly used in food supplements [1]regulator. According to Ruokavirasto (the Finnish Food Authority), there is no list of permitted or banned substances in food supplements other than vitamins and minerals: the product must be safe, its ingredients must have a history of use, and they must not make the product a medicine [31]regulator. Ruokavirasto's food supplement guidance does not name L-carnitine [30, 31]regulator.
• Health claims. The packaging or marketing of a food supplement may not make claims about treating or preventing disease [30]regulator. EFSA did not consider the claims submitted for L-carnitine on recovery, endurance, cholesterol or sperm production to be established [1]regulator.
• Ordering from abroad. According to Ruokavirasto, the law does not as such restrict ordering food supplements from abroad for personal use, but the products must meet EU requirements, and it is worth checking Fimea's medicines list that the product contains no substances classified as medicines in Finland. Receiving medicinal products by post from outside the EEA is prohibited [31]regulator.

This is not legal advice. Disclaimer.

Is L-carnitine doping?

Not as a substance: the WADA 2026 Prohibited List does not name L-carnitine [32]regulator. The route of administration can still be prohibited. Under section M2.2, intravenous infusions or injections of more than 100 ml in total per 12 hours are prohibited at all times, except those legitimately received in the course of hospital treatment, surgical procedures or clinical diagnostic investigations [32, 33]regulator.

According to the Finnish-language list by SUEK, salt, sugar, iron and nutrient solutions and some permitted medicines given into a vein as an infusion of more than 100 ml are not named on the list as such. The infusion is still prohibited if the volume exceeds 100 ml in 12 hours [33]regulator.

How to judge the quality of an L-carnitine product

Study results do not tell you what a particular product contains. In the single-dose study, the researchers measured the actual L-carnitine content of the capsules they used, and it was 86% of the amount stated by the manufacturer [26]B.

According to Ruokavirasto, buying a food supplement online from an unknown seller can be a risk, and when ordering online it is worth finding out whether the product may be considered a medicine in Finland [30]regulator. On reading a certificate of analysis (COA): How to read a COA and check a test result.

The future: what comes next?

ClinicalTrials.gov lists L-carnitine trials that are recruiting participants (as of 15 Oct 2026). Registry records are not peer-reviewed [37, 38, 39]E, not peer-reviewed.

• Heart failure and the kidneys. A 20-patient feasibility study of L-carnitine taken by mouth; the primary measures are whether patients can be recruited and whether they stay in the study. Estimated completion 12/2026 [37]E, not peer-reviewed.
• Muscle mass during GLP-1 weight loss. A randomised, placebo-controlled trial of a combination product containing carnitine, with 144 participants planned [38]E, not peer-reviewed.
• Fertility treatment. A randomised trial of the effect of carnitine on the number and quality of eggs in IVF, with 70 women planned [39]E, not peer-reviewed.

FAQ

Read the research yourself: sources

Every source opens the original publication or the regulator's page. The level shows what the source itself reports.

1. EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific Opinion on the substantiation of health claims related to L-carnitine and faster recovery from muscle fatigue after exercise, skeletal muscle tissue repair, increase in endurance capacity, maintenance of normal blood LDL-cholesterol concentrations, contribution to normal spermatogenesis, "energy metabolism", and increasing L-carnitine concentrations and/or decreasing free fatty acids in blood during pregnancy pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal. 2011;9(6):2212. EFSA Journal regulator
2. Evans AM, Fornasini G. Pharmacokinetics of L-carnitine. Clin Pharmacokinet. 2003;42(11):941-67. PMID 12908852 (review)
3. Longo N. Primary Carnitine Deficiency and Newborn Screening for Disorders of the Carnitine Cycle. Ann Nutr Metab. 2016;68 Suppl 3:5-9. PMID 27931018 (review)
4. Crefcoeur LL, Visser G, Ferdinandusse S, et al. Clinical characteristics of primary carnitine deficiency: A structured review using a case-by-case approach. J Inherit Metab Dis. 2022;45(3):386-405. PMID 34997761 (review)
5. U.S. National Library of Medicine, DailyMed. CARNITOR (levocarnitine) tablets and oral solution: prescribing information (Leadiant Biosciences; label version published 14 Nov 2024). DailyMed official
6. U.S. National Library of Medicine, DailyMed. CARNITOR (levocarnitine) injection: prescribing information (Leadiant Biosciences; label version published 22 Nov 2023). DailyMed official
7. Pooyandjoo M, Nouhi M, Shab-Bidar S, et al. The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials. Obes Rev. 2016;17(10):970-6. PMID 27335245 A
8. Askarpour M, Hadi A, Miraghajani M, et al. Beneficial effects of l-carnitine supplementation for weight management in overweight and obese adults: An updated systematic review and dose-response meta-analysis of randomized controlled trials. Pharmacol Res. 2020;151:104554. PMID 31743774 A
9. Mirrafiei A, Jayedi A, Shab-Bidar S. The Effects of L-Carnitine Supplementation on Weight Loss, Glycemic Control, and Cardiovascular Risk Factors in Patients With Type 2 Diabetes: A Systematic Review and Dose-response Meta-Analysis of Randomized Controlled Trials. Clin Ther. 2024;46(5):404-410. PMID 38594107 A
10. DiNicolantonio JJ, Lavie CJ, Fares H, et al. L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis. Mayo Clin Proc. 2013;88(6):544-51. PMID 23597877 A
11. Iliceto S, Scrutinio D, Bruzzi P, et al. Effects of L-carnitine administration on left ventricular remodeling after acute anterior myocardial infarction: the L-Carnitine Ecocardiografia Digitalizzata Infarto Miocardico (CEDIM) Trial. J Am Coll Cardiol. 1995;26(2):380-7. PMID 7608438 A
12. Tarantini G, Scrutinio D, Bruzzi P, et al. Metabolic treatment with L-carnitine in acute anterior ST segment elevation myocardial infarction. A randomized controlled trial. Cardiology. 2006;106(4):215-23. PMID 16685128 A
13. Wall BT, Stephens FB, Constantin-Teodosiu D, et al. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. J Physiol. 2011;589(Pt 4):963-73. PMID 21224234 A
14. Mielgo-Ayuso J, Pietrantonio L, Viribay A, et al. Effect of Acute and Chronic Oral l-Carnitine Supplementation on Exercise Performance Based on the Exercise Intensity: A Systematic Review. Nutrients. 2021;13(12):4359. PMID 34959912 (review)
15. Yarizadh H, Shab-Bidar S, Zamani B, et al. The Effect of L-Carnitine Supplementation on Exercise-Induced Muscle Damage: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. J Am Coll Nutr. 2020;39(5):457-468. PMID 32154768 A
16. Sawicka AK, Renzi G, Olek RA. The bright and the dark sides of L-carnitine supplementation: a systematic review. J Int Soc Sports Nutr. 2020;17(1):49. PMID 32958033 (review)
17. Lenzi A, Sgrò P, Salacone P, et al. A placebo-controlled double-blind randomized trial of the use of combined l-carnitine and l-acetyl-carnitine treatment in men with asthenozoospermia. Fertil Steril. 2004;81(6):1578-84. PMID 15193480 A
18. Sigman M, Glass S, Campagnone J, et al. Carnitine for the treatment of idiopathic asthenospermia: a randomized, double-blind, placebo-controlled trial. Fertil Steril. 2006;85(5):1409-14. PMID 16600222 A
19. Wei G, Zhou Z, Cui Y, et al. A Meta-Analysis of the Efficacy of L-Carnitine/L-Acetyl-Carnitine or N-Acetyl-Cysteine in Men With Idiopathic Asthenozoospermia. Am J Mens Health. 2021;15(2):15579883211011371. PMID 33906513 A
20. Michaelsen MP, Poulsen M, Bjerregaard AA, et al. The Effect of Dietary Supplements on Male Infertility in Terms of Pregnancy, Live Birth, and Sperm Parameters: A Systematic Review and Meta-Analysis. Nutrients. 2025;17(10):1710. PMID 40431450 A
21. Cruciani RA, Zhang JJ, Manola J, et al. L-carnitine supplementation for the management of fatigue in patients with cancer: an eastern cooperative oncology group phase III, randomized, double-blind, placebo-controlled trial. J Clin Oncol. 2012;30(31):3864-9. PMID 22987089 A
22. Marx W, Teleni L, Opie RS, et al. Efficacy and Effectiveness of Carnitine Supplementation for Cancer-Related Fatigue: A Systematic Literature Review and Meta-Analysis. Nutrients. 2017;9(11):1224. PMID 29112178 A
23. Nishioka N, Luo Y, Taniguchi T, et al. Carnitine supplements for people with chronic kidney disease requiring dialysis. Cochrane Database Syst Rev. 2022;12(12):CD013601. PMID 36472884 A
24. Koeth RA, Wang Z, Levison BS, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nat Med. 2013;19(5):576-85. PMID 23563705 C
25. Samulak JJ, Sawicka AK, Hartmane D, et al. L-Carnitine Supplementation Increases Trimethylamine-N-Oxide but not Markers of Atherosclerosis in Healthy Aged Women. Ann Nutr Metab. 2019;74(1):11-17. PMID 30485835 B
26. Krims-Davis K, Ozola M, Razzivina V, et al. Low Bioavailability and High TMAO Production: Novel Insights Into Acetylcarnitine and Carnitine Metabolism. Mol Nutr Food Res. 2025;69(24):e70316. PMID 41243468 B
27. Hathcock JN, Shao A. Risk assessment for carnitine. Regul Toxicol Pharmacol. 2006;46(1):23-8. PMID 16901595 (review)
28. European Medicines Agency. Article 57 product data (EMA/518502/2018 Rev.90, data as of 9 Oct 2026): levocarnitine entries in 12 EU countries and Northern Ireland; none for Finland and no centrally authorised (EU) product. EMA regulator
29. Finland. Lääkeluettelo (Fimea medicines list), decision 230/2025, sections 1-2 and annex 1 ("Levokarnitiini"). Finlex regulator
30. Ruokavirasto (Finnish Food Authority). Ravintolisät: neuvoja kuluttajille (food supplements: advice for consumers). Ruokavirasto regulator
31. Ruokavirasto (Finnish Food Authority). Usein kysyttyä ravintolisistä (frequently asked questions on food supplements). Ruokavirasto regulator
32. World Anti-Doping Agency. 2026 Prohibited List (in force 1 Jan 2026), section M2.2; L-carnitine is not named on the list. WADA (PDF) regulator
33. Finnish Center for Integrity in Sports (SUEK). Dopingaineryhmät ja -aineet 2026 (prohibited substances and methods 2026, based on the WADA list), section M2.2 and note 9. SUEK regulator
34. Cao Y, Qu HJ, Li P, et al. Single dose administration of L-carnitine improves antioxidant activities in healthy subjects. Tohoku J Exp Med. 2011;224(3):209-13. PMID 21701126 B
35. Samulak JJ, Sawicka AK, Samborowska E, et al. Plasma Trimethylamine-N-oxide following Cessation of L-carnitine Supplementation in Healthy Aged Women. Nutrients. 2019;11(6):1322. PMID 31200429 B
36. Sawicka AK, Jaworska J, Brzeska B, et al. L-Carnitine Combined with Leucine Supplementation Does Not Improve the Effectiveness of Progressive Resistance Training in Healthy Aged Women. J Nutr Health Aging. 2022;26(10):945-953. PMID 36259583 B
37. ClinicalTrials.gov. NCT07201714: Oral Carnitine in Heart Failure Patients (London Health Sciences Centre Research Institute OR Lawson Research Institute of St. Joseph's; early phase 1; recruiting; 20 participants planned; primary outcomes recruitment and retention rate; estimated primary completion 31 Dec 2026). Registry record, not peer-reviewed. ClinicalTrials.gov E, not peer-reviewed
38. ClinicalTrials.gov. NCT07393360: Effect of a Food for Special Medical Purposes on Muscle Mass Preservation During GLP-1 RAs Weight Loss Treatment (Pharmanutra S.p.a.; product with essential amino acids, carnitine, arginine and minerals; randomised, placebo; recruiting; 144 participants planned; estimated primary completion Dec 2026). Registry record, not peer-reviewed. ClinicalTrials.gov E, not peer-reviewed
39. ClinicalTrials.gov. NCT07783399: The Effects of Carnitine Supplementation on Oocytes in Women Undergoing IVF Process (The Obstetrics and Gynaecology Clinic Narodni Front; randomised; recruiting; 70 participants planned). Registry record, not peer-reviewed. ClinicalTrials.gov E, not peer-reviewed

Research and authority sources checked on 15 Oct 2026.

Evidence levels: A = randomised human trial or meta-analysis · B = observational human study or case series · C = animal study · D = cell or laboratory study · E = not peer-reviewed · regulator = a regulator's assessment or decision, not research evidence. The marker official means official product information (summary of product characteristics or label); it is not research evidence. For a review, the level shows what kind of research the statement rests on. No level: statements that something has not been studied, reviews' interpretations, named hypotheses and the general rules in our certificate-of-analysis guide.

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