Carnitine (L-carnitine, L-carnitine L-tartrate, acetyl-L-carnitine)
Summary
Healthy people make enough carnitine, so no intake is set. Pooled trials show a modest extra weight loss of about 1.2 kg with L-carnitine. Exercise results are mixed: some small trials found better high-intensity performance, others none. Only about 14–18% of supplemental L-carnitine is absorbed, and around 3 g/day can cause stomach upset and fishy body odor.
Key facts
- L-carnitine and acetyl-L-carnitine (the two main supplement forms), L-carnitine L-tartrate, and propionyl-L-carnitine (including glycine propionyl-L-carnitine)[1][6]
- No head-to-head human outcome data comparing forms in our sources. Absorption of supplemental L-carnitine is about 14–18%, much lower than from food[1]
- Body weight ↓ modest (B); high-intensity exercise performance ↑ in one small 24-week trial (D); mood scores ↓ in a heterogeneous meta-analysis of acetyl-L-carnitine (C)[2][4][7]
- No DRI: healthy people synthesize enough. The body needs about 15 mg/day; omnivorous diets supply about 24–145 mg/day and vegan diets about 1.2 mg/day[1]
- No UL. About 3 g/day can cause nausea, vomiting, cramps, diarrhea and a fishy body odor[1]
- 4 graded human outcomes on this page
- October 8, 2026
How it works
EstablishedCarnitine is an essential cofactor that transports long-chain fatty acids into mitochondria for oxidation to ATP, and helps move some toxic compounds out (established). About 95% of body carnitine is stored in heart and skeletal muscle. In exercise it may spare muscle glycogen, promote fat oxidation and lower lactate (proposed); raising muscle carnitine by diet took 24 weeks of L-carnitine with carbohydrate in one trial.[1][4]
What the human research says
Human trials only, one row per outcome. The form column shows what each trial actually tested. Grades follow our evidence-grading policy.
At a glance: strongest evidence per outcome
| Outcome | Grade | Effect | Strongest evidence | Rows |
|---|---|---|---|---|
| Metabolic | Grade B | Worsened | Meta-analysis · n = 2,292 · 2020 | 1 row |
| Stress | Grade C | Worsened | Meta-analysis · n = 791 · 2018 | 1 row |
| Performance | Grade D | No effect | Open-label · n = 24 · 2016 | 2 rows |
Every graded row
| Outcome | Effect | Grade | Best evidence | PMID |
|---|---|---|---|---|
| Body weight, BMI and fat mass | Worsened | Grade B | Meta-analysis · n = 2,292 · 2020 Adults in 37 randomized controlled trials Form: L-carnitine · Dose: Varied; maximum effect at about 2,000 mg/day in dose-response analysis · Duration: Varied across trials L-carnitine reduced body weight by about 1.2 kg, BMI by 0.24 kg/m² and fat mass by about 2.1 kg versus control. Waist circumference and body-fat percentage did not change. High-quality trials alone confirmed the weight effect; authors note it especially in adults with overweight or obesity. | 32359762 (opens PubMed)Source [2] |
| Mood: depressive symptom scores (acetyl-L-carnitine) | Worsened | Grade C | Meta-analysis · n = 791 · 2018 Adults with depressive symptoms in 12 randomized controlled trials (mean age 54) Form: acetyl-L-carnitine · Dose: Varied across trials · Duration: Varied across trials Across 9 placebo or no-treatment trials, acetyl-L-carnitine lowered depressive symptom scores (SMD -1.10), with very high heterogeneity (I² 86%). Effects appeared largest in older adults. | 29076953 (opens PubMed)Source [7] |
| Performance and muscle energy stores in vegetarians and omnivores | No effect | Grade D | Open-label trial · n = 24 · 2016 Male vegetarians (16) and omnivores (8) Form: L-carnitine · Dose: 2 g/day · Duration: 12 weeks L-carnitine raised plasma carnitine in both groups and muscle carnitine in vegetarians (13%), but maximal oxygen uptake, peak workload and muscle energy stores did not change. | 25612929 (opens PubMed)Source [5] |
| Muscle carnitine and high-intensity exercise performance | Improved | Grade D | RCT · n = 14 · 2011 Healthy young men Form: L-carnitine L-tartrate plus 80 g carbohydrate vs carbohydrate alone · Dose: 2 g L-carnitine L-tartrate with 80 g carbohydrate twice daily · Duration: 24 weeks Muscle carnitine rose 21% with carnitine and was unchanged in controls; muscle glycogen use at low intensity was 55% lower, and work output in the performance trial rose 11% from baseline with no change in controls. | 21224234 (opens PubMed)Source [4] |
Forms
| Form | Elemental % | Absorption (human data) | GI tolerance | Studied for |
|---|---|---|---|---|
| L-carnitine (base) | 100%[1] | About 14–18% of supplemental L-carnitine is absorbed, much less than from food (ODS).[1] | About 3 g/day can cause nausea, vomiting, abdominal cramps, diarrhea and a fishy body odor.[1] | Weight-loss and exercise trials |
| L-carnitine L-tartrate (LCLT) | Varies[4] | No head-to-head human data in our sources. Taken with carbohydrate for 24 weeks, it raised muscle carnitine 21%.[4] | No form-specific tolerance data in our sources.[1] | Exercise metabolism and recovery |
| Acetyl-L-carnitine (ALCAR) | Varies[1] | No head-to-head human data in our sources.[1] | No significant difference in adverse events versus placebo in the 2003 Cochrane review.[8] | Mood and cognition trials (1–3 g/day) |
| Propionyl-L-carnitine / glycine propionyl-L-carnitine (GPLC) | Varies[1] | No head-to-head human data in our sources.[6] | No form-specific tolerance data in our sources.[1] | Some exercise trials |
Compound weight → elemental active
500 mg l-carnitine (base) ≈ 500 mg elemental active
Studied doses
Doses studied in human trials ranged from 1 to 4 g of L-carnitine a day, from single servings before exercise up to a year in weight-loss trials. In weight trials, the effect peaked near 2 g/day.[1][2][6]
Intake reference: No DRI: the Food and Nutrition Board concluded in 1989 that carnitine is not an essential nutrient because healthy people synthesize enough. The body needs about 15 mg/day from food and synthesis. No UL.[1] No tolerable upper intake level has been established; about 3 g/day can cause gastrointestinal effects and fishy body odor. NIH ODS fact sheet (updated April 17, 2023).
Interactions
Published interactions only: each row cites a source. No row means none was found in our sources, not that a combination is safe.
Who should be careful
- Higher doses
- Around 3 g/day can cause nausea, vomiting, abdominal cramps, diarrhea and a fishy body odor.[1]
- Kidney disease or seizure disorders
- ODS reports carnitine can cause muscle weakness in people with uremia and seizures in people with seizure disorders.[1]
- TMAO
- Gut bacteria can turn unabsorbed carnitine into TMAO, which might raise heart-disease risk; the effect seems larger in meat eaters, and its implications are not well understood.[1]
- Before you start
- Talk to your pharmacist or clinician before adding this supplement, especially if you take prescription medicines, are pregnant or breastfeeding, or have a chronic health condition.[1]
Talk to your pharmacist or clinician before starting a supplement, especially if you take prescription medicines.
Articles about Carnitine (L-carnitine, L-carnitine L-tartrate, acetyl-L-carnitine)
Plain-English answers to common questions, built on the evidence above.
Frequently asked questions
Does L-carnitine help with weight loss?
Pooled trials found a modest effect: about 1.2 kg more weight lost than control, with the largest effect near 2 g/day. ODS describes results as equivocal and says larger studies are needed, and one meta-analysis found the effect shrank over time.[2][3][1]
Does carnitine improve exercise performance?
Results are mixed. One 24-week trial of L-carnitine L-tartrate with carbohydrate raised muscle carnitine and work output, while a 12-week trial without carbohydrate found no performance change. A systematic review found benefits only for high-intensity exercise.[4][5][6][1]
Do vegetarians need carnitine supplements?
Vegan diets supply only about 1.2 mg/day, but the body makes enough for healthy people. In one trial, vegetarians had lower blood carnitine but normal muscle stores, and supplements did not change their performance.[1][5]
What about acetyl-L-carnitine for memory?
A 2003 meta-analysis found benefits in mild cognitive decline, but a 2003 Cochrane review found benefit only on clinical global impression and none on objective measures, and ODS calls the effects unclear.[9][8][1]
How much is absorbed?
Only about 14–18% of supplemental L-carnitine is absorbed, much less than carnitine from food; excess in the blood is excreted in urine.[1]
Sources
- [1]Carnitine: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2023. fact-sheet
- [2]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.. Clin Nutr ESPEN, 2020. meta-analysis
- [3]The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials.. Obes Rev, 2016. meta-analysis
- [4]Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans.. J Physiol, 2011. RCT
- [5]Effect of L-carnitine supplementation on the body carnitine pool, skeletal muscle energy metabolism and physical performance in male vegetarians.. Eur J Nutr, 2016. open-label
- [6]Effect of Acute and Chronic Oral l-Carnitine Supplementation on Exercise Performance Based on the Exercise Intensity: A Systematic Review.. Nutrients, 2021. systematic-review
- [7]Acetyl-L-Carnitine Supplementation and the Treatment of Depressive Symptoms: A Systematic Review and Meta-Analysis.. Psychosom Med, 2018. meta-analysis
- [8]Acetyl-L-carnitine for dementia.. Cochrane Database Syst Rev, 2003. systematic-review
- [9]Meta-analysis of double blind randomized controlled clinical trials of acetyl-L-carnitine versus placebo in the treatment of mild cognitive impairment and mild Alzheimer's disease.. Int Clin Psychopharmacol, 2003. meta-analysis
What changed
- First draft. Every evidence-row PMID checked with NCBI E-utilities (esummary + efetch abstract) and re-read in an independent adversarial pass.