Library / Peptides / Metabolic & Body Composition / L-Carnitine
Strong evidence · Grade A

L-Carnitine

Metabolic & Body Composition
Evidence
Strong Evidence
Route
Oral, Intramuscular injection, or Intravenous
Frequency
Oral: 1-2x daily; IV/IM: 1-3x weekly
Category
Metabolic & Body Composition
TL;DR
L-Carnitine is a naturally occurring amino acid derivative synthesized from lysine and methionine, primarily in the liver and kidneys. Its primary biological role is transporting long-chain fatty acids into mitochondria for beta-oxidation (fat burning).
Part 01 · How it works

Mechanism.

L-Carnitine is a naturally occurring amino acid derivative synthesized from lysine and methionine, primarily in the liver and kidneys. Its primary biological role is transporting long-chain fatty acids into mitochondria for beta-oxidation (fat burning). L-Carnitine is available in several forms including L-carnitine tartrate, acetyl-L-carnitine (ALCAR), and propionyl-L-carnitine, each with somewhat different clinical applications. It is well-studied with decades of clinical data.

L-Carnitine works like a ferry service that carries fat molecules across the mitochondrial membrane — the wall surrounding your cell's power plant. Without enough ferries, fat piles up on one side and can't be burned for energy, no matter how much exercise you do.

Mechanism · technical
L-Carnitine functions as an essential cofactor for the carnitine palmitoyltransferase (CPT) system, which shuttles long-chain fatty acyl-CoA molecules across the inner mitochondrial membrane for beta-oxidation. Without carnitine, cells cannot efficiently burn fat for energy. Acetyl-L-carnitine additionally supports acetylcholine synthesis and has neuroprotective properties. L-Carnitine also helps buffer excess acyl groups and maintain the CoA/acyl-CoA ratio, supporting overall mitochondrial function and reducing oxidative stress.
Part 02 · Dosing & administration

How it's taken.

Clinical · trial-validated

Values below describe how L-Carnitine has been administered in human clinical trials and/or approved labeling. Provided for educational purposes only — this is not medical advice and not instructions for self-administration. Consult your healthcare provider before making any health decision.

Standard dose
500-2000 mg oral; 600-1000 mg IV/IM
Oral, Intramuscular injection, or Intravenous · Oral: 1-2x daily; IV/IM: 1-3x weekly
Duration
Ongoing as needed
·
An FDA-approved prescription form (levocarnitine / Carnitor) exists and oral 500–2000 mg/day is supported by human RCTs — hence a clinical dose basis.
·
The approved indication is carnitine deficiency (incl. dialysis-associated); the aesthetic "fat-burning" IV/IM use at these doses is off-label.
·
Acetyl-L-carnitine is preferred for cognitive endpoints, L-carnitine L-tartrate for exercise/recovery — match the form to the goal.
Need help with reconstitution?

Use the free peptide calculator for dilution, unit conversion, and injection volume.

Open calculator
Part 03 · Safety

Side effects, rare serious events, who shouldn't.

Reported side effects
Oral L-carnitine is generally well tolerated. The most common side effects are GI symptoms including nausea, diarrhea, abdominal cramps, and a fishy body odor at higher doses. There is some concern that gut bacteria can convert L-carnitine to TMAO (trimethylamine-N-oxide), which has been associated with cardiovascular risk, though the clinical significance remains debated. Injectable L-carnitine may cause injection site pain. **Recent research (2026):** A pharmacovigilance analysis of EudraVigilance reports found L-carnitine adverse events were most often gastrointestinal, skin, and nervous-system disorders, with serious cases in about 34% of reports (Di Mauro D, Calapai F, Ammendolia I et al., DOI: 10.3390/nu18111716).
Absolute · do not use
×
Known hypersensitivity to L-carnitine or any component
×
Seizure disorders (high doses may lower seizure threshold in susceptible individuals)
×
Hypothyroidism (may interfere with thyroid hormone action)
Interactions
Warfarin
L-carnitine may potentiate warfarin's anticoagulant effect; monitor INR
Moderate
Thyroid hormones (levothyroxine)
L-carnitine may inhibit thyroid hormone entry into cells, reducing thyroid hormone efficacy
Moderate
Anticonvulsants (valproic acid)
Valproic acid depletes carnitine; supplementation may be beneficial but requires monitoring
Minor
Labs to monitor
CMP (Comprehensive Metabolic Panel)
Baseline and every 6 months
Liver and kidney function (carnitine is renally excreted)
Free and Total Carnitine Levels
Baseline (optional)
Assess baseline status and supplementation adequacy
Lipid Panel
Baseline and every 3 months
Track lipid metabolism effects
TMAO Level (optional)
Baseline (optional, research context)
Carnitine can be metabolized to TMAO by gut bacteria, associated with cardiovascular risk
Part 04 · Evidence

How strong is the evidence?

Scores derived from rating, indexed studies, regulatory status, and catalogued safety data for this peptide. Curated per-peptide scoring replaces this when available.

86
Grade A
Grade A. Evidence is strongest where indications match regulatory approval — pair with a clinician when applying beyond label.
Clinical efficacy
Rating reflects consistent peer-reviewed evidence in its indication.
86
Study quality
9 indexed studies in our dataset. Designs vary — see Research log for per-study grades.
90
Regulatory clarity
FDA-approved for at least one indication.
90
Safety profile
Based on 3 documented contraindications, 3 interactions, 4 lab checkpoints.
88
Long-term data
Years of post-approval surveillance available.
74
Part 05 · Research log

Every study we cite.

Each study with its published finding and a plain-language note on limitations or funding.

01
2024
0
L-carnitine supplementation in recovery from exercise
L-carnitine supplementation reduced muscle damage markers and improved recovery after exercise
Meta-analysis of RCTs; moderate evidence quality
PMID 37460208 ↗
02
2019
0
Acetyl-L-carnitine for peripheral neuropathy
ALC showed modest improvement in nerve conduction and pain in diabetic neuropathy
Meta-analysis; heterogeneous study designs
PMID 31118753 ↗
03
2026
0
L-carnitine-SIRT3 axis in kidney fibrosis (preclinical)
In mice, hyperoside reduced kidney fibrosis via an ACAT1-L-carnitine-SIRT3 axis; L-carnitine partially restored mitochondrial function when ACAT1 was knocked down.
04
2026
0
Acetyl-L-carnitine in mood disorders (meta-analysis)
A systematic review and meta-analysis (15 studies; 809 participants) reported that acetyl-L-carnitine significantly reduced depressive symptoms versus placebo, with efficacy comparable to standard antidepressants and fewer adverse effects.
05
2026
0
L-carnitine and sperm redox balance (fish study)
In a fish-feeding study, dietary L-carnitine (150 mg/kg) improved thawed-sperm motility and reduced lipid peroxidation, attributed to enhanced sperm lipid integrity.
06
2026
0
L-carnitine and lipids in women with obesity, meta-analysis (2026)
A meta-analysis of 10 randomized trials in women with overweight or obesity reported L-carnitine supplementation was associated with modest reductions in triglycerides, total cholesterol and LDL-C, with no significant change in HDL-C.
07
2026
0
L-carnitine in a reproductive-toxicity rat model (2026)
In a rat model of atrazine-induced reproductive toxicity, L-carnitine, especially a niosomal formulation, was associated with improved sperm quality and testicular markers. Preclinical (animal) evidence only.
08
2026
0
L-carnitine in an IBS rat model (2026)
In a rat model of irritable bowel syndrome, oral L-carnitine dose-dependently reduced visceral hypersensitivity and colonic hyperpermeability, an effect linked to orexin signaling. Preclinical (animal) evidence only.
09
2026
0
L-carnitine safety, pharmacovigilance analysis (2026)
A pharmacovigilance analysis of the EudraVigilance database found L-carnitine adverse-event reports were most often gastrointestinal, skin and nervous-system related, with a lower proportion of serious cases than for coenzyme Q10.
Part 06 · Cost & access

Where you can get it.

Regulatory status
L-Carnitine is widely available as a dietary supplement without a prescription. Levocarnitine (Carnitor) is FDA-approved for the treatment of primary and secondary carnitine deficiency, including carnitine deficiency in dialysis patients. Injectable L-carnitine is available through clinics and compounding pharmacies.
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Part 07 · Your appointment

Questions to bring.

01
Which form of carnitine (L-carnitine, ALCAR, propionyl-L-carnitine) is best for my goals?
02
What is the optimal dose and timing relative to exercise?
03
Should I have my carnitine levels tested, especially if I'm on dialysis or a vegetarian?
04
How does L-carnitine interact with my thyroid medication?
05
Is injectable L-carnitine significantly more effective than oral?
06
What is the evidence regarding TMAO production from L-carnitine supplementation?
References

Every citation, numbered.

Citation list. For our editorial read of each study — including bias flags and quality grades — see the Research log above.

  1. 01.
    L-carnitine supplementation in recovery from exercise · 2024 · PMID 37460208 ↗
  2. 02.
    Acetyl-L-carnitine for peripheral neuropathy · 2019 · PMID 31118753 ↗
  3. 03.
    L-carnitine-SIRT3 axis in kidney fibrosis (preclinical) · 2026
  4. 04.
    Acetyl-L-carnitine in mood disorders (meta-analysis) · 2026
  5. 05.
    L-carnitine and sperm redox balance (fish study) · 2026
  6. 06.
    L-carnitine and lipids in women with obesity, meta-analysis (2026) · 2026
  7. 07.
    L-carnitine in a reproductive-toxicity rat model (2026) · 2026
  8. 08.
    L-carnitine in an IBS rat model (2026) · 2026
  9. 09.
    L-carnitine safety, pharmacovigilance analysis (2026) · 2026