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L-carnitine supplement: does it help weight loss or workouts?

By the Life in Good Form editors. Updated 2026-10-15.

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What carnitine is

The ODS explains that carnitine is a nutrient found in many foods that your body also makes. It helps turn food into energy, and most of it is stored in muscles. Because healthy people make enough, carnitine is not an essential nutrient and has no recommended daily amount.

Red meat is a good source. Poultry, fish and dairy have some, while vegetables, fruits and grains have very little. The body absorbs carnitine from food much better than from supplements.

Who might be low in carnitine

• Babies born prematurely
• People with end-stage kidney disease
• People on kidney dialysis
• People with primary carnitine deficiency, a rare genetic disorder

Some medicines also lower carnitine, including long-term use of certain antibiotics such as pivampicillin and anticonvulsants such as phenobarbital and valproic acid. Anyone in these groups should be guided by their doctor.

What the research shows

Weight loss. One 6-month study in adults with type 2 diabetes found no effect. Another found people taking the weight-loss drug orlistat plus carnitine for 1 year lost about 4 pounds more than those on orlistat alone. Other studies also found only small differences.

Exercise. Some small studies found improved endurance or faster recovery, but others did not. In one study, carnitine did not change 1-hour cycling performance but slightly raised muscle carnitine in men on vegetarian diets.

Blood sugar and fertility details

Blood sugar. Some small studies found carnitine might help the body use insulin better and lower blood glucose and A1C. Others found it lowered cholesterol but not triglycerides in people with diabetes. The ODS says these studies were small and more research is needed.

Fertility. Several studies found carnitine improved sperm health in men with infertility, but it did not raise successful pregnancy rates in their partners. In women with PCOS, one study found higher ovulation and pregnancy rates and lower miscarriage risk when carnitine was added to an infertility drug, while another small study found better cycle regularity and ovulation but no change in miscarriage risk.

Heart health and other uses

• Heart. Some studies suggest carnitine may lower the risk of irregular heartbeats and angina but not heart failure or heart attack. Others found that taking it for 6 months or longer might increase heart disease risk.
• Peripheral artery disease. Some studies found less leg pain when walking; others found no benefit.
• PCOS. Small studies reported better ovulation and pregnancy rates with carnitine, sometimes with an infertility drug.
• Osteoarthritis. One small study found less knee pain in middle-aged women; another in women with obesity found no improvement.
• Dementia. A few studies suggest help in mild cases; others show short-term or no effects.

Safety

• High doses. 3 grams or more a day can cause nausea, vomiting, stomach cramps, diarrhea and a fishy body odor.
• Kidney disease. High amounts can cause muscle weakness in people with chronic kidney disease.
• Seizure disorders. High amounts can raise seizure risk.
• Thyroid. NOW Foods' label specifically flags thyroid disorders.
• Food is safe. Carnitine from food has no upper limit.

How to choose an L-carnitine supplement

• Forms. The ODS says the two main supplement forms are L-carnitine and acetyl-L-carnitine.
• Label amount. NOW Foods' L-Carnitine 500 mg provides 500 mg L-carnitine (from 746 mg L-carnitine tartrate) per capsule, 1 to 3 times daily.
• Stay under 3 g a day to avoid digestive side effects and fishy odor.
• Liquids and powders are also sold; measure carefully.
• Talk with your doctor if you have kidney disease, seizures, thyroid disease or heart disease.

What to look for when you buy

Questions people ask

Does L-carnitine help weight loss?

Only slightly. ODS reports small differences of only a few pounds, such as about 4 pounds over a year with orlistat.

Do I need L-carnitine supplements?

Most healthy people make enough. Premature babies, people on dialysis and those with rare genetic deficiency may be low.

What are L-carnitine side effects?

At 3 grams or more a day: nausea, vomiting, cramps, diarrhea and a fishy body odor.

L-carnitine or acetyl-L-carnitine?

Both are main supplement forms. See our acetyl-L-carnitine guide for that form.

Is L-carnitine safe for the heart?

Results are mixed. Some studies suggest taking it for 6 months or longer might increase heart disease risk.

Sources

• Carnitine: Fact Sheet for Consumers (ods.od.nih.gov), NIH Office of Dietary Supplements
• L-Carnitine 500 mg Veg Capsules (www.nowfoods.com/products/supplements/l-carnitine-500-mg-veg-capsules), NOW Foods

Sources checked 2026-10-15.