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Nutrient compound (not a peptide)Human trialsFDA approved

L-Carnitine (injection)

Levocarnitine

Last reviewed October 27, 2026 · 21 sources · Written for general readers · Compare with another compound →

The bottom line

L-carnitine is a natural nutrient that carries fat into the parts of cells that burn it, and the prescription form Carnitor is FDA approved only for carnitine deficiency. In dozens of trials, mostly with pills, people lost only about 1 kg more than with placebo, workout results were inconsistent, and a large trial found no help for fatigue. Gut bacteria also turn it into TMAO, a compound linked to heart disease, so more is not automatically better.

Where the evidence stands

What it is

L-carnitine is a natural compound the body makes in the liver, kidneys and brain. It is also found in red meat and other animal foods.[1] It is not a peptide.

Healthy people make enough on their own, and U.S. nutrition experts do not consider it an essential nutrient for healthy people.[1]

A prescription form called levocarnitine is sold as Carnitor. The injection is FDA approved for carnitine deficiency caused by certain inherited metabolic diseases, and for people with kidney failure on dialysis.[2]

Carnitine shots offered for weight loss or energy are being used outside these approved uses.[2] In 2025 FDA also warned Amazon about a carnitine product sold with fat dissolving claims, calling it an unapproved new drug.[3]

Name
L-Carnitine (injection) (Levocarnitine)
Other names
levocarnitine, Carnitor, acetyl L-carnitine (related form)
Type
Nutrient compound (not a peptide)
Formula
C7H15NO3
Molecular weight
About 161.2 g/mol

What it does in the body

L-carnitine is made naturally in the body and eaten in meat. Its main job is to act as a shuttle that carries long chain fats into mitochondria, the parts of cells that burn fuel, so muscle and heart can use fat for energy.[4][1]

This is the biology, area by area. A change measured in the body, like a higher blood level, does not always mean a person feels a benefit. The claims check below covers that.

Energy and cells

Well established

Inside cells, carnitine carries long chain fatty acids across the walls of mitochondria so they can be burned. In some inherited diseases it also binds toxic leftovers so the body can flush them out.[4] This is textbook biology and the basis for the drug's approval.

Muscle and strength

Measured in people

Muscle does not soak up extra carnitine easily. In healthy young men, muscle carnitine rose about 21% only after 24 weeks of taking it by mouth with a sugary drink, and about 20% after 12 weeks in another trial.[5][6] An IV drip raised muscle carnitine about 15% in five hours, but only while insulin was also held high.[7] With higher muscle carnitine, men used about 55% less stored muscle sugar during moderate exercise and made about 44% less lactate during hard exercise.[5]

Fat and appetite

Measured in people

In a 12 week trial of 12 men, those whose muscle carnitine rose burned about 6% more energy and gained no fat, while the control group gained about 1.8 kg of fat on the same sugary drink.[6] In 14 older men, raising muscle carnitine over 25 weeks raised fat burning during exercise by about 20%.[8] Across 37 trials, the extra weight loss averaged only about 1.2 kg.[9]

Gut

Measured in people

Carnitine that is not absorbed is broken down by gut bacteria into TMA, which the liver turns into TMAO.[10] Meat eaters made more than 20 times as much TMAO from a test dose as vegans and vegetarians, and taking carnitine for a month raised TMAO in both groups.[11]

Heart and blood vessels

Measured in people

Heart muscle burns fat for fuel, and carnitine helps deliver it.[4] In 9 patients with mitochondrial disease who took carnitine pills for at least three months, blood TMAO rose about 12 fold on average.[12] High TMAO is linked to heart disease, and in mice extra carnitine sped artery plaque through gut bacteria.[10]

Kidneys

Measured in people

Dialysis removes carnitine from the blood, which is why the injection is approved for people on dialysis.[2] A pooled analysis of 49 trials with 1,734 dialysis patients found carnitine lowered a blood inflammation marker called CRP, but did not change hemoglobin, the amount of anemia drug needed, or most blood fats.[13]

Nerves

Measured in people

A related form, acetyl L-carnitine, was tested to protect nerves during breast cancer chemotherapy in 409 women. Instead of helping, it made nerve damage scores worse at 24 weeks than placebo did.[14]

How it works

Carnitine acts like a shuttle that carries fat into mitochondria, the parts of cells that burn fuel.

  • It moves long chain fatty acids into mitochondria so muscle and heart cells can burn them for energy.[4]
  • In some inherited diseases, it also binds toxic byproducts so the body can flush them out.[4]
  • Muscle takes up extra carnitine slowly, and studies that raised muscle levels needed months of intake with carbohydrate, or high insulin during an IV drip.[5][7]
  • Gut bacteria turn unabsorbed carnitine into TMAO, a compound linked to clogged arteries, especially in meat eaters.[1][10][11]

The fat shuttle role is well established. Whether extra carnitine makes healthy people burn meaningfully more fat is not.

What the research shows

We keep animal and human evidence apart. A result in animals is a reason to study something in people, not proof that it works in people.

Animal and lab studies

Animal data raise a heart health question

  • In mice, carnitine added to the diet changed the mix of gut bacteria and sharply raised blood levels of TMA and TMAO.[10]
  • Those mice developed more artery plaque, the fatty buildup behind heart attacks. When antibiotics wiped out their gut bacteria, the extra plaque did not appear.[10]
  • In mice with normal gut bacteria, carnitine, choline or TMAO in the diet slowed the body's removal of cholesterol from tissues.[10]

Limit: These are mouse results from one main study, and their meaning for people is still debated. Unlike many compounds on this site, carnitine has far more human data than animal data.

Human studies

Proven for deficiency, small or mixed for everything else

  • Carnitor is FDA approved to treat true carnitine deficiency, including in people on dialysis.[2][4]
  • Weight: a 2016 review of 9 controlled trials with 911 adults found about 1.3 kg more weight loss than controls, and the effect got smaller the longer people took it.[15]
  • Weight: a 2020 review of 37 trials with 2,292 people found about 1.2 kg more weight loss and 2.1 kg more fat loss, but no change in waist size or body fat percent.[9]
  • Muscle fuel: in 14 healthy young men over 24 weeks, carnitine pills taken with a sugary drink raised muscle carnitine about 21%. During moderate exercise they used about 55% less stored muscle sugar, and work output in a 30 minute test rose about 11%.[5]
  • Fat gain: in 12 men over 12 weeks, the carnitine group burned about 6% more energy and gained no fat, while men taking the sugary drink alone gained about 1.8 kg of fat.[6]
  • Training: in 21 young men on 24 weeks of interval training (14 finished), carnitine raised muscle carnitine about 30% but gave no extra gain in fitness, power or work output beyond training alone.[16]
  • Older men: in 14 men around age 69 over 25 weeks, carnitine raised muscle carnitine about 20% and fat burning during exercise about 20%, with no change in how insulin handled blood sugar.[8]
  • Fatigue: in 376 people with cancer and fatigue, four weeks of carnitine pills did no better than placebo.[17]
  • Heart: a pooled analysis of 13 trials with 3,629 heart attack patients found about 27% fewer deaths with carnitine, but heart failure and repeat heart attacks did not change.[18]
  • Dialysis: across 49 trials with 1,734 dialysis patients, carnitine lowered the inflammation marker CRP, but did not improve anemia or most blood fats, and no side effects were reported.[13]
  • TMAO: meat eaters made more than 20 times as much TMAO from carnitine as vegans and vegetarians, and a month of carnitine raised TMAO in both groups.[11] In 9 patients with mitochondrial disease, three months or more of pills raised TMAO about 12 fold.[12]
  • We found no strong trials showing that carnitine injections cause weight loss in healthy people.

Limit: Most trials used pills, many were small, and few tested the injected wellness form.

Claims check

The most common claims about this compound, and what studies actually found. Verdicts rate the evidence, not whether you should use it.

Burns fat and causes weight loss

Mixed results

A 2016 review of 9 controlled trials with 911 adults found carnitine users lost about 1.3 kg more than placebo, and the effect shrank over time.[15] A 2020 review of 37 trials with 2,292 people found about 1.2 kg more weight loss and 2.1 kg more fat loss, with no change in waist size or body fat percent.[9] In a small 12 week study of 12 men, carnitine prevented the fat gain seen with a sugary drink alone.[6] Most trials used pills. The injected wellness shots have not been tested for weight loss.

Improves workouts and endurance

Mixed results

A 2018 review found inconsistent results across 11 trials in 251 trained athletes and 17 studies in 237 recreationally active adults.[1] In 14 young men, work output in a 30 minute test rose about 11% after 24 weeks of carnitine with carbohydrate, with no change in controls.[5] But in 21 men doing 24 weeks of interval training, adding carnitine gave no extra gain in fitness or power over training alone.[16]

Boosts energy and fights fatigue

No benefit in trials so far

In a placebo controlled trial of 376 people with cancer related fatigue, four weeks of carnitine pills raised blood carnitine, but fatigue improved just as much on placebo. Even people who were low in carnitine at the start did not do better.[17]

Improves blood sugar

Mixed results

A 2023 pooled analysis of 41 trials with about 2,900 adults found small drops in fasting blood sugar, insulin resistance and HbA1c, a three month sugar average.[1] An earlier pooled analysis of four trials in people with type 2 diabetes found no change in HbA1c.[1] In 14 older men, 25 weeks of carnitine did not change how well insulin cleared sugar from the blood.[8]

Protects the heart

Mixed results

A 2013 pooled analysis of 13 trials with 3,629 heart attack patients found about 27% fewer deaths and 65% fewer dangerous heart rhythms with carnitine, but no change in heart failure or repeat heart attacks.[18] On the other side, carnitine raises TMAO in people, and high TMAO is linked to heart disease.[11][10]

Boosts male fertility

Mixed results

A 2022 Cochrane review of six trials with 1,089 men found better sperm movement and count at some time points, but no effect on pregnancy or live birth rates.[1] A 2022 network analysis of 23 antioxidant trials with 1,917 men ranked carnitine first for sperm movement, about 6.5 percentage points better than placebo.[19]

Sharpens memory

Mixed results

A 2003 analysis of 21 trials with 1,204 adults with mild memory problems or early Alzheimer's found better test scores with acetyl L-carnitine. A Cochrane review found benefits at 12 and 24 weeks but not at one year, no effect on daily function, and said routine use was not justified.[1]

Treats carnitine deficiency

Shown in people

Levocarnitine is FDA approved to treat carnitine deficiency from inherited metabolic diseases and to prevent and treat deficiency in people on dialysis.[2] The label notes its effect on symptoms and outcomes in dialysis patients has not been established.[2]

Known risks and side effects

  • Serious allergic reactions. The Carnitor injection label warns of serious allergic reactions, including swelling of the airway, some within minutes of an IV dose.[2]
  • Seizures. Seizures have been reported with both pill and IV forms, including in people with no seizure history, and seizures got worse in some people who already had them.[2]
  • Side effects seen in trials. In label trials in dialysis patients, headache (22% vs 16% on placebo) and high blood pressure (20% vs 14%) were more common with levocarnitine.[2] High intakes can cause nausea, vomiting, cramps, diarrhea and a fishy body odor.[1]
  • Heart, cholesterol and nerve questions. Gut bacteria turn carnitine into TMAO, which is linked to artery disease, and one trial found higher LDL cholesterol with carnitine.[1][11] In a cancer trial, the related acetyl form made chemotherapy nerve damage worse: 38% had a big drop in nerve scores versus 28% on placebo.[14]
  • Drug interactions and sport rules. The label reports higher INR, a blood clotting measure, in people on warfarin.[2] WADA's 2027 list still bans IV infusions or injections above a set volume within 12 hours outside hospital care, whatever is in them.[20]

Regulatory status

Today: Levocarnitine (Carnitor) is an FDA approved prescription drug for carnitine deficiency.[2] L-carnitine is also sold as a dietary supplement.[1] Using it for weight loss or energy is not an approved use, and FDA has treated a carnitine product sold with fat dissolving claims as an unapproved drug.[3] Plain levocarnitine does not appear on FDA's list of substances nominated for compounding, while the related acetyl L-carnitine is still under review there.[21]

  1. FDA warns Amazon that an L-carnitine ampoule sold to dissolve fat is an unapproved new drug.[3]
  2. FDA's updated 503A nomination list keeps acetyl L-carnitine under evaluation for compounding.[21]
  3. The 2027 WADA list takes effect and keeps its limit on large IV infusions for athletes.[20]

Sources

  1. NIH Office of Dietary Supplements. Carnitine: Fact Sheet for Health Professionals. Updated April 17, 2023. NIH ODS
  2. DailyMed. CARNITOR (levocarnitine) injection, solution. Leadiant Biosciences. Label updated November 2023. DailyMed label
  3. U.S. Food and Drug Administration. Warning Letter to Amazon.com, Inc. (MARCS-CMS 695821). March 3, 2025. FDA warning letter
  4. DailyMed. CARNITOR (levocarnitine) tablet. Leadiant Biosciences. DailyMed label
  5. Wall BT, Stephens FB, Constantin-Teodosiu D, Marimuthu K, Macdonald IA, Greenhaff PL. 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):963-973. PMID 21224234
  6. Stephens FB, Wall BT, Marimuthu K, Shannon CE, Constantin-Teodosiu D, Macdonald IA, et al. Skeletal muscle carnitine loading increases energy expenditure, modulates fuel metabolism gene networks and prevents body fat accumulation in humans. J Physiol. 2013;591(18):4655-4666. PMID 23818692
  7. Stephens FB, Constantin-Teodosiu D, Laithwaite D, Simpson EJ, Greenhaff PL. An acute increase in skeletal muscle carnitine content alters fuel metabolism in resting human skeletal muscle. J Clin Endocrinol Metab. 2006;91(12):5013-5018. PMID 16984983
  8. Chee C, Shannon CE, Burns A, Selby AL, Wilkinson D, Smith K, et al. Increasing skeletal muscle carnitine content in older individuals increases whole-body fat oxidation during moderate-intensity exercise. Aging Cell. 2021;20(2):e13303. PMID 33464721
  9. Talenezhad N, Mohammadi M, Ramezani-Jolfaie N, Mozaffari-Khosravi H, Salehi-Abargouei A. Effects of l-carnitine supplementation on weight loss and body composition: A systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis. Clin Nutr ESPEN. 2020;37:9-23. PMID 32359762
  10. 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):576-585. PMID 23563705
  11. Koeth RA, Lam-Galvez BR, Kirsop J, Wang Z, Levison BS, Gu X, et al. l-Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans. J Clin Invest. 2019;129(1):373-387. DOI 10.1172/JCI94601
  12. Vallance HD, Koochin A, Branov J, Rosen-Heath A, Bosdet T, Wang Z, et al. Marked elevation in plasma trimethylamine-N-oxide (TMAO) in patients with mitochondrial disorders treated with oral l-carnitine. Mol Genet Metab Rep. 2018;15:130-133. PMID 30023305
  13. Chen Y, Abbate M, Tang L, Cai G, Gong Z, Wei R, et al. L-Carnitine supplementation for adults with end-stage kidney disease requiring maintenance hemodialysis: a systematic review and meta-analysis. Am J Clin Nutr. 2014;99(2):408-422. PMID 24368434
  14. Hershman DL, Unger JM, Crew KD, Minasian LM, Awad D, Moinpour CM, et al. Randomized double-blind placebo-controlled trial of acetyl-L-carnitine for the prevention of taxane-induced neuropathy in women undergoing adjuvant breast cancer therapy. J Clin Oncol. 2013;31(20):2627-2633. PMID 23733756
  15. Pooyandjoo M, Nouhi M, Shab-Bidar S, Djafarian K, Olyaeemanesh A. 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):970-976. PMID 27335245
  16. Shannon CE, Ghasemi R, Greenhaff PL, Stephens FB. Increasing skeletal muscle carnitine availability does not alter the adaptations to high-intensity interval training. Scand J Med Sci Sports. 2018;28(1):107-115. PMID 28345160
  17. Cruciani RA, Zhang JJ, Manola J, Cella D, Ansari B, Fisch MJ. 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):3864-3869. PMID 22987089
  18. DiNicolantonio JJ, Lavie CJ, Fares H, Menezes AR, O'Keefe JH. L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis. Mayo Clin Proc. 2013;88(6):544-551. PMID 23597877
  19. Li KP, Yang XS, Wu T. The Effect of Antioxidants on Sperm Quality Parameters and Pregnancy Rates for Idiopathic Male Infertility: A Network Meta-Analysis of Randomized Controlled Trials. Front Endocrinol (Lausanne). 2022;13:810242. PMID 35265037
  20. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2027. Comes into effect January 1, 2027. WADA 2027 Prohibited List
  21. U.S. Food and Drug Administration. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act. Updated May 14, 2026. FDA 503A nominations list
Medical disclaimer

This page is educational information only. It is not medical advice and does not replace care from a licensed medical provider. Do not use this page to decide whether to take any substance. Talk to a licensed medical provider first.

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