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.

Values below describe how L-Carnitine has been administered in published trials and 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

FDA-approved prescription form (Carnitor/levocarnitine) for carnitine deficiency. OTC supplement forms widely available. Acetyl-L-carnitine preferred for cognitive effects, L-carnitine L-tartrate for exercise performance.

Need help with reconstitution?

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

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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.
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.

82
Grade B
Grade B. 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
2 indexed studies in our dataset. Designs vary — see Research log for per-study grades.
71
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
2018
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 29344834 ↗
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 31220358 ↗
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?