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Research · Supplements

L-carnitine

Meta-analyses find L-carnitine lowered body weight about 1.2 to 1.3 kg more than control, mostly in adults with overweight, with the effect shrinking over time. Soreness fell after hard exercise in 7 trials. Muscle carnitine rose only when taken with 80 g of carbohydrate for 24 weeks. Carnitine raised blood TMAO tenfold in one trial.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement in the US. Levocarnitine is also an FDA-approved prescription drug (Carnitor) for primary systemic carnitine deficiency.
Also called
carnitine, levocarnitine, L-carnitine L-tartrate, LCLT, acetyl-L-carnitine, ALCAR, propionyl-L-carnitine, Carnitor
Taken for
fat loss, fat burning, endurance, recovery, less soreness, energy

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help2

Reported risks2

What people take it for, and what was found

Shown to help2

Strong

Weight and fat loss

Shown to lower body weight about 1.2 kg in adults, mostly with overweight or obesity. Body fat percentage did not change, and the effect shrank over time.

The numbers and sources
Effect
Across 37 RCTs (2,292 participants), L-carnitine lowered body weight by 1.21 kg (95% CI -1.73 to -0.68), BMI by 0.24 kg/m² and fat mass by 2.08 kg (95% CI -3.44 to -0.72), with no change in waist circumference or body fat percentage. Only the weight effect held in high-quality trials [1]. In 9 RCTs (911 adults), weight fell 1.33 kg more than control (95% CI -2.09 to -0.57), and the effect shrank the longer people took it (p = 0.002) [2]. An umbrella meta-analysis pooling 8 meta-analyses (16,352 participants) found lower weight (ES -1.11, 95% CI -1.90 to -0.33), BMI (ES -0.33) and waist circumference (ES -1.34, 95% CI -1.83 to -0.85) [3].
Population
Adults, mostly with overweight or obesity [1][2]. Trials of 8 to 30 weeks at 150 to 4,000 mg a day [3].
Sources
[1], [2], [3]
Caveats
Body fat percentage did not change [1]. The reviews differ on waist circumference [1][3]. Heterogeneity was high for weight and BMI in the umbrella analysis (I² 90.6% and 89.8%) [3].
Moderate

Muscle soreness and damage markers

Shown to lower muscle soreness for up to 96 hours after damaging exercise in adults, with damage markers lower at 24 hours only.

The numbers and sources
Effect
Across 7 RCTs, L-carnitine lowered muscle soreness at 0, 24, 48, 72 and 96 hours after damaging exercise, and lowered creatine kinase, myoglobin and LDH at 24 hours only [4].
Population
Adults after exercise-induced muscle damage [4].
Sources
[4]
Caveats
The abstract gives no effect sizes. Seven trials.

Mixed results1

Limited

Endurance and exercise metabolism

Limited evidence: some small trials reported better endurance, one only with added carbohydrate, while a CrossFit trial found no change.

The numbers and sources
Effect
In 30 publications in healthy people, carnitine raised blood carnitine and changed resting VO2, with no change in blood lactate at rest or after exercise [5]. In 14 healthy men, 2 g of L-carnitine L-tartrate with 80 g of carbohydrate twice daily for 24 weeks raised muscle carnitine 21%, cut muscle glycogen use 55% at low intensity, and raised work output 11% from baseline; carbohydrate alone did not change it [6]. A 2026 systematic review of 18 randomized placebo-controlled trials in active people reported better endurance performance after single doses of 2 to 15 g and after 2 to 3 g a day for 2 to 24 weeks, with no change in fat oxidation during exercise [7]. In 20 trained men, 3 g of L-carnitine L-tartrate 90 minutes before a 20-minute CrossFit workout did not change repetitions completed (202.4 against 204.5) [8].
Population
Healthy adults [5]; 14 young men [6]; active people in 18 trials [7]; 20 recreational CrossFit athletes [8].
Sources
[5], [6], [7], [8]
Caveats
The single trial is small, and the carbohydrate was needed to raise insulin and move carnitine into muscle [6]. The meta-analysis reports dose in "g/dL", which appears to be a unit error [5]. The 2026 review did not pool results, and none of its trials was at low risk of bias [7].

Doses studied

Weight loss trials suggested the largest effect near 2,000 mg a day in a dose-response model [1]. The muscle carnitine trial used 2 g of L-carnitine L-tartrate with 80 g of carbohydrate twice daily for 24 weeks [6]. The performance meta-analysis linked blood carnitine changes to 1 to 2 (units printed as g/dL) taken for 3 to 4 weeks [5]. A kidney safety review describes up to 6,000 mg a day as generally tolerated in healthy adults, without trials in athletes [9].

Risks

Reported risks2

LimitedHow often is not known

TMAO and cardiovascular markers

Limited evidence: L-carnitine raised blood TMAO tenfold in older women without changing inflammation or lipids. The heart disease link is from mice and observational data.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In mice, carnitine supplements raised TMAO and increased atherosclerosis, which did not occur when gut bacteria were suppressed. In 2,595 people having cardiac evaluation, plasma carnitine predicted cardiovascular disease and major adverse cardiac events only when TMAO was also high. Omnivores produced more TMAO than vegans after carnitine [10]. In healthy older women, 24 weeks of L-carnitine raised plasma TMAO tenfold but did not change CRP, IL-6, adhesion molecules or lipids [11]. In healthy volunteers given 0.5 or 1.5 g of carnitine or acetylcarnitine, about 90% of both was metabolized to TMAO, with plasma levels reaching 50 µM [12].
Population
Mice and observational cohorts [10]; healthy older women [11]; healthy volunteers given single doses [12].
Sources
[10], [11], [12]
Caveats
The heart disease link is from animals and observational data. The one supplement trial measured markers, not events, for 24 weeks.
LimitedStudied in menHow often is not known

Trouble sleeping

One small trial found 10% of trained men reported trouble sleeping after a 3 g dose, with no placebo rate given.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In the CrossFit trial, 10% of participants reported difficulty sleeping after 3 g of L-carnitine L-tartrate [8].
Population
20 trained men [8].
Sources
[8]
Caveats
One small single-dose trial. The abstract does not give a placebo rate [8].

Checked, no increase found1

Limited

Kidney effects

One trial found no change in kidney markers after 12 weeks of L-carnitine in overweight and obese adults.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 68 overweight and obese adults randomized to control, 1,000 mg of L-carnitine a day, exercise, or both for 12 weeks, creatinine and urea did not change significantly in any group [13]. A review of 8 carnitine studies in athletes and bodybuilders found that kidney risks and benefits have not been evaluated in that group [9].
Population
68 overweight and obese adults, mean age 29, for 12 weeks [13]. Athletes and bodybuilders [9].
Sources
[13], [9]
Caveats
One small trial with blood markers only, at one dose, with no placebo capsule. The review is narrative, and no study in athletes was located [9].

Claims tested and not found

  1. That carnitine lowers body fat percentage. Fat percentage did not change across 37 RCTs [1].
  2. That carnitine burns more fat during exercise. Fat oxidation did not change after single doses or 2 to 4 weeks of use across 18 trials [7].
  3. That carnitine alone loads muscle. Muscle carnitine rose only with 80 g of carbohydrate twice daily over 24 weeks in the trial that measured it [6].

Sources

  1. Talenezhad N, Mohammadi M, Ramezani-Jolfaie N, et al. 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. Clinical Nutrition ESPEN. 2020. https://doi.org/10.1016/j.clnesp.2020.03.008
  2. 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. Obesity Reviews. 2016. https://doi.org/10.1111/obr.12436
  3. Hamedi-Kalajahi F, Zarezadeh M, Malekahmadi M, et al. The Effect of the L-Carnitine Supplementation on Obesity Indices: An Umbrella Meta-Analysis. International Journal for Vitamin and Nutrition Research. 2025. https://doi.org/10.31083/ijvnr40033
  4. 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. Journal of the American College of Nutrition. 2020. https://doi.org/10.1080/07315724.2019.1661804
  5. Vecchio M, Chiaramonte R, Testa G, et al. Clinical Effects of L-Carnitine Supplementation on Physical Performance in Healthy Subjects, the Key to Success in Rehabilitation: A Systematic Review and Meta-Analysis from the Rehabilitation Point of View. Journal of Functional Morphology and Kinesiology. 2021. https://doi.org/10.3390/jfmk6040093
  6. 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. Journal of Physiology. 2011. https://doi.org/10.1113/jphysiol.2010.201343
  7. Eryiğit H, Güzel Y, Bulut S, et al. Acute and Chronic L-Carnitine Supplementation Enhances Endurance Performance Without Consistent Effects on Substrate Oxidation in Active Individuals: A Systematic Review. International Journal of Sport Nutrition and Exercise Metabolism. 2026. https://doi.org/10.1123/ijsnem.2026-0077
  8. Devrim-Lanpir A, Velasco LS, Ramirez Lara FG, et al. Acute L-Carnitine Supplementation Does Not Improve CrossFit Performance: A Randomized, Double-Blind, Placebo-Controlled Crossover Study. Nutrients. 2025. https://doi.org/10.3390/nu17172784
  9. Davani-Davari D, Karimzadeh I, Sagheb MM, et al. The Renal Safety of L-Carnitine, L-Arginine, and Glutamine in Athletes and Bodybuilders. Journal of Renal Nutrition. 2019. https://doi.org/10.1053/j.jrn.2018.08.014
  10. Koeth RA, Wang Z, Levison BS, et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis. Nature Medicine. 2013. https://doi.org/10.1038/nm.3145
  11. Samulak JJ, Sawicka AK, Hartmane D, et al. L-Carnitine Supplementation Increases Trimethylamine-N-Oxide but not Markers of Atherosclerosis in Healthy Aged Women. Annals of Nutrition and Metabolism. 2018. https://doi.org/10.1159/000495037
  12. Krims-Davis K, Ozola M, Razzivina V, et al. Low Bioavailability and High TMAO Production: Novel Insights Into Acetylcarnitine and Carnitine Metabolism. Molecular Nutrition & Food Research. 2025. https://doi.org/10.1002/mnfr.70316
  13. Samsudin N, Ahmad NS, Ooi FK, et al. Protective Effects of L-Carnitine Supplement Combined with Interval Training on Kidney and Liver Function among Overweight and Obese Individuals. International Journal of Preventive Medicine. 2026. https://doi.org/10.4103/ijpvm.ijpvm_381_24

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