L-Carnitine: Benefits, Uses, and Side Effects

A picture of a sports bottle of L-Carnitine in a gym, there are people in the background working out.
L-Carnitine: Benefits, Uses, and Side Effects
Date Published: 07/25/2023
Date Modified: 09/14/2023
A picture of a sports bottle of L-Carnitine in a gym, there are people in the background working out.

We take a look at popular supplement, L-carnitine and the research and potential side effects behind it.


What Is L-Carnitine?

L-carnitine is a compound that the human body naturally synthesizes from the amino acids lysine and methionine [1]. It serves a crucial role in energy metabolism, aiding in the transportation of long-chain fatty acids into the mitochondria. These fatty acids are then oxidized to generate energy [2]. As a dietary supplement, L-carnitine has several potential benefits and possible side effects.

Reported benefits of L-carnitine

General benefits of L-carnitine may include weight management, improved exercise performance, improved heart health, better brain function, and improved blood sugar regulation.

L-carnitine is believed to enhance fat metabolism, which can help in weight management efforts [3]. However, scientific evidence is mixed, and more comprehensive research is needed.

L-carnitine might enhance exercise performance. It potentially helps reduce muscle damage, improves oxygen supply to muscles, increases blood flow, and hastens recovery after intense workouts [4].

L-carnitine supplements might have cardiovascular benefits. They have been reported to reduce symptoms of angina and peripheral vascular disease, and they may improve outcomes for people with serious heart conditions, such as coronary heart disease or heart failure [5].

Some studies indicate that L-carnitine could help maintain brain function and potentially slow the progression of Alzheimer’s disease and other neurodegenerative conditions [6].

Preliminary research suggests that L-carnitine might help maintain healthy blood sugar levels and improve insulin sensitivity in people with diabetes [7].

Despite these potential benefits, it’s worth noting that L-carnitine supplementation is typically unnecessary for healthy people who consume a balanced diet. The human body can naturally produce sufficient L-carnitine, and it is available through dietary sources, such as red meat and dairy products [2].

Is L-carnitine good for women?

L-carnitine may specifically benefit women who are pregnant or breastfeeding, undergoing menopause, or experiencing polycystic ovary syndrome.

During pregnancy and breastfeeding, the body’s requirement for L-carnitine may increase. However, women should not take L-carnitine supplements during pregnancy or while breastfeeding without consulting with a healthcare provider due to the lack of safety data [8].

Some preliminary research has suggested that L-carnitine might help reduce some symptoms of menopause, such as fatigue and hot flashes. More research is needed to confirm these potential benefits [9, 10].

Some research has suggested that L-carnitine might be helpful in managing some symptoms of PCOS, a hormonal disorder common among women of reproductive age [11].

What are the disadvantages of L-carnitine?

L-carnitine can produce side effects, including digestive problems, body odor, seizures, potential heart risks, and allergic reactions.

L-carnitine supplementation can cause gastrointestinal issues in some people, including nausea, vomiting, abdominal cramps, and diarrhea. A unique side effect of L-carnitine supplementation is a “fishy” body odor, which is caused by the buildup and excretion of a substance called trimethylamine in sweat and urine [12].

There have been rare reports of seizures in individuals taking L-carnitine, both with and without pre-existing seizure disorders. However, it’s unclear whether L-carnitine was the direct cause of these seizures [13].

Some research has suggested a possible connection between L-carnitine supplementation and increased risk of atherosclerosis, a condition in which the arteries harden due to buildup of fats, cholesterol, and other substances. This is potentially linked to increased levels of a compound called TMAO in the blood [14].

As with any substance, some people might have an allergic reaction to L-carnitine. Symptoms can include difficulty breathing, hives, and swelling of the face, lips, tongue, or throat [12].

Is it good to take L-carnitine every day?

Whether or not it’s beneficial to take L-carnitine every day depends on individual health conditions, dietary habits, and specific health goals. L-carnitine is generally considered safe for most adults when taken in recommended dosages [15].

For healthy People who consume a balanced diet, additional supplementation with L-carnitine is typically not necessary. The appropriate dosage of L-carnitine can depend on the specific reason for taking it along with health status, age, and weight. Typically, doses can range from about 500 to 2000 milligrams per day, split into two or three doses [15].

However, there isn’t an established Recommended Dietary Allowance (RDA) for L-carnitine, as the body is typically able to produce enough L-carnitine if there is enough protein in the diet. Therefore, it is not considered an essential nutrient, which is why an RDA or Reference Intake (RI) has not been established [15].

According to the Office of Dietary Supplements, there is currently no established Tolerable Upper Intake Level (UL) for L-carnitine. However, it’s worth noting that doses above 3 grams per day produce more serious side effects [15].

It is always recommended to consult healthcare providers before starting any new supplementation regimen, as they can provide guidance based on individual health needs and conditions.


[1] Brass, E.P. Supplemental Carnitine and Exercise. Am J Clin Nutr 2000, 72, 618S-623S

[2] Rebouche, C.J.; Paulson, D.J. Carnitine Metabolism and Function in Humans. 2003, 6, 41–66

[3] 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. Obesity Reviews 2016, 17, 970–976

[4] Fielding, R.; Riede, L.; Lugo, J.P.; Bellamine, A. L-Carnitine Supplementation in Recovery after Exercise. Nutrients 2018, Vol. 10, Page 349 2018, 10, 349

[5] DiNicolantonio, J.J.; Lavie, C.J.; Fares, H.; Menezes, A.R.; O’Keefe, J.H. L-Carnitine in the Secondary Prevention of Cardiovascular Disease: Systematic Review and Meta-Analysis. Mayo Clin Proc 2013, 88, 544–551

[6] HroudovΓ‘, J.; FiΕ‘ar, Z.; KitzlerovΓ‘, E.; ZverovΓ‘, M.; Raboch, J. Mitochondrial Respiration in Blood Platelets of Depressive Patients. Mitochondrion 2013, 13, 795–800

[7] Malaguarnera, M.; Vacante, M.; Avitabile, T.; Malaguarnera, M.; Cammalleri, L.; Motta, M. L-Carnitine Supplementation Reduces Oxidized LDL Cholesterol in Patients with Diabetes. Am J Clin Nutr 2009, 89, 71–76

[8] Manta-Vogli, P.D.; Schulpis, K.H.; Dotsikas, Y.; Loukas, Y.L. The Significant Role of Carnitine and Fatty Acids during Pregnancy, Lactation and Perinatal Period. Nutritional Support in Specific Groups of Pregnant Women. Clinical Nutrition 2020, 39, 2337–2346

[9] Clark, R.M.; Balakrishnan, A.; Waters, D.; Aggarwal, D.; Owen, K.Q.; Koo, S.I. L-Carnitine Increases Liver Alpha-Tocopherol and Lowers Liver and Plasma Triglycerides in Aging Ovariectomized Rats. J Nutr Biochem 2007, 18, 623–628

[10] Hernandes, V.V.; Dordevic, N.; Hantikainen, E.M.; Sigurdsson, B.B.; SmΓ‘rason, S.V.; Garcia-Larsen, V.; GΓΆgele, M.; Caprioli, G.; Bozzolan, I.; Pramstaller, P.P.; et al. Age, Sex, Body Mass Index, Diet and Menopause Related Metabolites in a Large Homogeneous Alpine Cohort. Metabolites 2022, 12, 205

[11] Ismail, A.M.; Hamed, A.H.; Saso, S.; Thabet, H.H. Adding L-Carnitine to Clomiphene Resistant PCOS Women Improves the Quality of Ovulation and the Pregnancy Rate. A Randomized Clinical Trial. European Journal of Obstetrics and Gynecology and Reproductive Biology 2014, 180, 148–152

[12] Rebouche, C.J. Kinetics, Pharmacokinetics, and Regulation of l-Carnitine and Acetyl-l-Carnitine Metabolism. Ann N Y Acad Sci 2004, 1033, 30–41

[13] Zeiler, F.A.; Sader, N.; Gillman, L.M.; West, M. Levocarnitine Induced Seizures in Patients on Valproic Acid: A Negative Systematic Review. Seizure 2016, 36, 36–39

[14] Koeth, R.A.; Wang, Z.; Levison, B.S.; Buffa, J.A.; Org, E.; Sheehy, B.T.; Britt, E.B.; Fu, X.; Wu, Y.; Li, L.; et al. Intestinal Microbiota Metabolism of L-Carnitine, a Nutrient in Red Meat, Promotes Atherosclerosis. Nat Med 2013, 19, 576–585

[15] Carnitine – Health Professional Fact Sheet

About the author

Stephen Rose

Chris is one of the writers at Lifespan.io. His interest in regenerative medicine and aging emerged as his personal training client base grew older and their training priorities shifted. He started his masters work in Bioengineering at Harvard University in 2013 and is currently completing his PhD at SUNY Polytechnic University in Albany, NY. His dissertation is focused on the role of the senescent cell burden in the development of fibrotic disease. His many interests include working out, molecular gastronomy, architectural design, and herbology.