Metabolic & weight
L-carnitine (levocarnitine)
Also called levocarnitine, carnitine, Carnitor, Carnitor SF, acetyl-L-carnitine (related form), propionyl-L-carnitine (related form)
L-carnitine is a small nutrient the body makes from two amino acids and also gets from meat. It carries fats into mitochondria so they can be burned for energy. As a prescription drug (levocarnitine, brand Carnitor) it is FDA-approved to treat carnitine deficiency, and it is also sold widely as a supplement for fat loss and exercise, where the evidence is modest.
Overview
L-carnitine is a small nutrient the body makes from two amino acids and also gets from meat. It carries fats into mitochondria so they can be burned for energy. As a prescription drug (levocarnitine, brand Carnitor) it is FDA-approved to treat carnitine deficiency, and it is also sold widely as a supplement for fat loss and exercise, where the evidence is modest.
How it works
Established: carnitine acts as a shuttle that moves long-chain fatty acids across the inner membrane of mitochondria, where they are broken down for energy. When carnitine is missing, as in genetic transporter defects, some inborn errors of metabolism or in dialysis patients, fat cannot be used properly and harmful fatty compounds build up. Proposed: extra carnitine in people with normal levels may modestly improve fat use, blood sugar control or exercise recovery, but trial results are mixed.
What research shows
- FDA labels: approved for primary systemic carnitine deficiency, secondary deficiency from inborn errors of metabolism, and (injection) prevention and treatment of deficiency in dialysis patients with end-stage kidney disease.
- Weight loss: a 2016 meta-analysis of 9 RCTs (911 adults) found about 1.33 kg more weight loss than placebo; weight was a secondary outcome in most trials.
- Type 2 diabetes/insulin resistance: a 2023 meta-analysis of 41 trials (about 2,900 people) found lower fasting glucose, insulin resistance and HbA1c at 0.25–4 g/day.
- Heart: a 2013 meta-analysis of 13 trials after heart attack (3,629 adults) found lower all-cause death and arrhythmias, but no effect on heart failure or repeat heart attack.
- Exercise: a 2021 review of 11 trials found mixed results, with some gains in high-intensity measures and none for moderate-intensity performance.
Doses studied in people
| Study or label | Dose used | Source |
|---|---|---|
| FDA label (Carnitor tablets) — carnitine deficiency, adults | 990 mg two or three times daily by mouth | 1 |
| FDA label (Carnitor tablets/oral solution) — infants and children | 50–100 mg/kg/day in divided doses, maximum 3 g/day | 1 |
| FDA label (Carnitor oral solution) — adults | 1–3 g/day (for a 50 kg person), starting at 1 g/day | 1 |
| FDA label (Carnitor injection) — end-stage kidney disease on hemodialysis | Starting 10–20 mg/kg dry body weight IV after each dialysis session, adjusted by trough levels | 2 |
| FDA label (Carnitor injection) — metabolic disorders | 50 mg/kg IV, given in divided doses every 3–4 hours (never less than every 6 hours) | 2 |
Doses listed are FDA label doses for diagnosed carnitine deficiency; supplement trials for weight or blood sugar used roughly 0.25–4 g/day, but there is no approved dose for those uses.
Read this first: these are the amounts given to participants in published studies or written on official prescribing labels, reported for reference. They are not recommendations. Trial doses were chosen for specific patients under medical supervision, and a dose that is safe in one person can be harmful in another.
Safety
- Common side effects (labels): nausea, vomiting, stomach cramps, diarrhea and a fishy body odor, often reduced with lower doses.
- Seizures have been reported with oral or IV use, including more frequent seizures in people with seizure disorders (labels).
- Serious allergic reactions, including anaphylaxis, have been reported with IV use, mostly in dialysis patients (label).
- Long-term high oral doses in severe kidney disease can build up trimethylamine (TMA) and TMAO; gut bacteria turn unabsorbed carnitine into TMAO, which is linked to heart disease risk, with uncertain significance.
- Can raise INR in people on warfarin (label); certain seizure drugs (e.g., valproic acid) lower carnitine levels.
Report side effects of any drug or product to the FDA through MedWatch. For a possible poisoning in the US, call Poison Control at 1-800-222-1222.
Legal status
- FDA
- FDA-approved as levocarnitine (Carnitor tablets 1985; oral solution and injection later) for carnitine deficiency and dialysis-related deficiency. L-carnitine is also legally sold as a dietary supplement.
- Compounding
- Levocarnitine is the active ingredient of approved drugs; it is not separately listed on FDA's 503A nominations list (May 14, 2026), while acetyl-L-carnitine is in 503A Category 1 (under evaluation).
- Sports (WADA)
- Not prohibited as a substance. However, IV infusions or injections of more than 100 mL per 12 hours are prohibited at all times (M2.2) unless given in hospital care, surgery or clinical tests.
- Other
- Not a controlled substance.
Rules change often. See Legal status of peptides for how these categories work.
Storage and stability
Per label: tablets and oral solution stored at controlled room temperature (25°C).
General lab handling, not instructions for personal use. See Storage and stability.
History
Carnitine was long recognized as a nutrient involved in fat metabolism. Levocarnitine tablets (Carnitor) were approved by the FDA in December 1985 for primary systemic carnitine deficiency, with an oral solution and an injection approved later; the injection is also approved for carnitine deficiency in people with end-stage kidney disease on dialysis. The US Food and Nutrition Board has not set intake recommendations because healthy people make enough. L-carnitine and related forms are now popular dietary supplements.
Common questions
Is L-carnitine FDA-approved?
Does L-carnitine help with weight loss?
Is L-carnitine banned in sport?
The substance itself is not banned, but IV infusions over 100 mL in 12 hours are prohibited outside hospital care 7.
Related compounds
AICAR (acadesine)
acadesine · AICA riboside
AICAR is a small molecule (a nucleoside, not a peptide) that tricks cells into acting as if they are low on energy, switching on an enzyme called AMPK.
SLU-PP-332
SLU-PP332 · (E)-4-hydroxy-N′-(naphthalen-2-ylmethylene)benzohydrazide
SLU-PP-332 is a lab-made small molecule (not a peptide) that switches on estrogen-related receptors, proteins that help muscles build mitochondria and burn fat.
NAD+
nicotinamide adenine dinucleotide · β-NAD
NAD+ is not a peptide but a small helper molecule that every cell uses to make energy and repair DNA.
MOTS-c
mitochondrial open reading frame of the 12S rRNA-c · MOTSc
MOTS-c is a small peptide made from instructions in mitochondrial DNA, the cell's 'power plant' genes.
Sources
- CARNITOR (levocarnitine) tablets and oral solution prescribing information (FDA, 2018) FDA label
- CARNITOR (levocarnitine) injection prescribing information (FDA, 2018) FDA label
- NIH Office of Dietary Supplements: Carnitine — Health Professional Fact Sheet PubMed review
- Pooyandjoo M et al. The effect of (L-)carnitine on weight loss in adults: systematic review and meta-analysis of RCTs. Obes Rev 2016 Journal
- DrugPatentWatch: NDA 018948 (Carnitor tablets) approval date Regulatory
- FDA: Bulk drug substances nominated for use in compounding under section 503A (updated May 14, 2026) Regulatory
- WADA Prohibited List Regulatory
Last reviewed 2026-10-26 · How we research · Found an error? See our corrections policy.