L-Carnitine
EVIDENCE: MODERATEAlso sold as: carnitine, L-carnitine base, acetyl-L-carnitine, L-carnitine L-tartrate
L-carnitine carries fatty acids into cells to be burned for energy. Meta-analyses of trials using 1–3 g a day found small drops in fasting glucose and HbA1c and about 1 kg more weight loss than placebo.
Compiled by iSupplementReviews editorial team ·Researched 2026-10-16 · 4 sources
- Type
- Amino acid derivative
- Studied dose
- 1–3 g/day
- Best form
- L-carnitine base, tartrate or acetyl-L-carnitine (depending on goal)
- Our rating
- MODERATE — Several human trials — limits in size, duration, or independence
What is L-carnitine?
L-carnitine is a compound made from amino acids that shuttles fatty acids into mitochondria, where they are burned for energy. It is sold for fat loss, exercise and blood sugar.
Other names and forms
L-carnitine base, L-carnitine L-tartrate (sports), acetyl-L-carnitine (brain and nerve research), propionyl-L-carnitine (circulation).
Where does L-carnitine come from?
Red meat and dairy, plus the body’s own production in the liver and kidneys.
How does L-carnitine work in the body?
Carnitine is needed to move long-chain fats into mitochondria. Healthy people make enough, so extra carnitine’s effects are modest; it may help more where levels are low.
What is L-carnitine claimed to do?
Burn fat, boost energy, improve insulin sensitivity and exercise recovery.
What does the research show?
| Claim | Evidence | Dose studied | Verdict |
|---|---|---|---|
| Fasting glucose and HbA1c | Meta-analysis of 37 RCTs | 1–3 g/day | Small positive |
| Weight loss | Meta-analysis | 1–3 g/day | Small positive |
| Exercise recovery | Smaller trials | 1–2 g/day | Mixed |
Blood sugar
Carnitine produced small reductions in fasting glucose and HbA1c across 37 trials. Fathizadeh et al. (2019) reported fasting glucose down about 4.6 mg/dL and HbA1c down about 0.3 points.
Weight
Carnitine added about 1.3 kg of weight loss versus placebo. Pooyandjoo et al. (2016) noted the effect shrank in longer trials.
What dose was studied?
| Goal | Dose | Duration |
|---|---|---|
| Glucose markers | 1–3 g/day | 8–24 weeks |
| Weight | 1–3 g/day | 4–24 weeks |
Side effects
Nausea, stomach upset, fishy body odor.
Drug interactions
- Warfarin and other blood thinners: may add to the anticoagulant effect (moderate).
- Thyroid hormone: one trial found carnitine counteracted thyroid hormone action, so people treated for an underactive thyroid should ask first (moderate).
Who should not take L-carnitine?
People with hypothyroidism, seizure disorders or on anticoagulants without medical advice. Gut bacteria convert carnitine to TMAO, which has been linked to atherosclerosis in research (Koeth et al., 2013).
What the authorities say
Memorial Sloan Kettering’s About Herbs entry warns that carnitine may add to the effect of warfarin and raise bleeding risk with other blood thinners. Carnitine is approved as a drug only for primary carnitine deficiency.
What to know about L-carnitine
L-carnitine has small benefits for glucose and weight at 1–3 g a day. Milligram amounts are a tiny fraction of those doses.
Frequently asked questions about L-Carnitine
Does L-carnitine lower blood sugar?
Slightly. A 2019 meta-analysis of 37 trials found carnitine lowered fasting glucose by about 4.6 mg/dL and HbA1c by about 0.3 percentage points, mostly at 1–3 g a day.
Does carnitine help weight loss?
A little. A 2016 meta-analysis found about 1.3 kg more weight loss than placebo, with the effect fading over time.
Is carnitine safe?
Generally, at 1–3 g a day. It can cause a fishy body odor, and gut bacteria convert it into TMAO, a compound studied as a possible heart-risk marker.
References
- [1]Fathizadeh H et al. — The effects of L-carnitine supplementation on glycemic control: a systematic review and meta-analysis of randomized controlled trials (EXCLI J, 2019)
- [2]Pooyandjoo M et al. — The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials (Obes Rev, 2016)
- [3]Koeth RA et al. — Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis (Nat Med, 2013)
- [4]Memorial Sloan Kettering Cancer Center — Carnitine (About Herbs database)
Products we reviewed containing L-Carnitine
Based on recorded labels or seller-described formulas. Inclusion does not establish a match to the strains, preparations or amounts studied here; check each review's disclosure limits.