L-carnitine
L-carnitine
Supplements. Modern nutrition.
Also called Carnitine, Levocarnitine, Acetyl-L-carnitine
Pinyin: zuǒ xuán ròu jiǎn
Spanish: L-carnitina
May clash with thyroid medicineA compound made from two amino acids that helps carry fats into cells to be burned for energy, and it is sold mainly for weight and exercise.
Did you know? Carnitine was first found in meat in 1905, and its name comes from the Latin word for flesh, carnis.
What it may help, and how strong the proof is
- Weight. Meta-analyses of randomized trials find a small weight loss, about 1 kilogram (2 pounds) on average. The effect is mostly in overweight people who also change diet or exercise, and it may fade over time.See the research: 180 studies in peoplePromising proof
- Blood pressure. In people on dialysis, a 2022 meta-analysis of 8 small trials found fewer blood pressure drops during treatment, mainly with oral doses. An older analysis did not find a clear effect, so results vary.See the research: 51 studies in peoplePromising proof
- Muscles & exercise. Carnitine is sold for muscle soreness and recovery. Evidence in healthy people is mixed, and for muscle cramps during dialysis the evidence is not strong enough to say whether it helps.See the research: 140 studies in peopleTraditional proof
Parts of the body
Traditional use
Carnitine has no folk history. It was found in meat extracts in the early 1900s and was later used in medicine for carnitine deficiency in people on dialysis.
How it is classified
How people take it
Weight trials used about 150 mg to 4 grams a day for 8 to 30 weeks. Doctors prescribe levocarnitine for carnitine deficiency, and the dose is set by a clinician. Acetyl-L-carnitine is a related form with its own research and is not the same product.
Capsule, tablet, powder and food.
Where to get it
The body makes carnitine from the amino acids lysine and methionine, mostly in the liver and kidneys. Food sources are red meat, poultry, fish and dairy, so vegetarians usually get less. Capsules, liquids and powders are sold in health stores and online.
Be careful
Common side effects are nausea, stomach upset, and a fishy body odor at higher doses. Carnitine may change how well thyroid medicine works, and it may raise INR (a blood clotting test) when taken with warfarin. Some anti-seizure drugs such as valproic acid lower the body's carnitine, so ask a doctor and get blood tests if you take these. Gut bacteria turn carnitine into a compound called TMAO, which some studies link to heart disease, though no cause has been proven.
Avoid if: thyroid disease; epilepsy (ask a doctor first); heart disease (ask a doctor first); pregnancy (not well studied).
Mixing with other things
- Works well together
Both support energy production in cells and are sold for energy and heart health. Their combined effects are not well studied.
- Use cautionThyroid medicine (levothyroxine (Synthroid))
Carnitine and thyroid hormone affect each other's metabolism, and carnitine may change how well thyroid medicine works. This is not well proven. Check thyroid levels if you start it.
- Use cautionBlood thinners (warfarin, Eliquis, Xarelto, Plavix, daily aspirin)
Levocarnitine labels note reports of higher INR with warfarin, and one case report involved a related blood thinner. Evidence is weak, but check INR if you take warfarin.
Adds up with others that may slow blood clotting: , , , , , , , , , , , , , and 47 more.
The honest take
The body makes its own carnitine, and food gives more. Doctors use prescription forms for carnitine deficiency, including in people on dialysis. Store products for weight and fat burning go further than the research, which shows only a small weight loss that may fade.
Sources
Each “See the research” link opens PubMed, the U.S. National Library of Medicine's index of medical studies, showing only trials and reviews done in people. The number tells you how much a use has been tested, not whether it worked. The proof rating tells you that.
Study counts checked October 2026.