L-Carnitine for Weight Loss: Dosage, Results and Side Effects

Shuttles long-chain fatty acids across the inner mitochondrial membrane for beta-oxidation. Healthy people synthesise enough from lysine and methionine and get more from meat, so supplementation is not correcting a shortage in most cases, which is why the effect sizes stay small.

• Body weight: a meta-analysis of 37 randomised trials with dose-response analysis found reductions in body weight of about 1.21 kg, BMI and fat mass.
• Male fertility: increased sperm concentration, motility and normal morphology against placebo in trials, with a 2025 meta-analysis of monotherapy for idiopathic male infertility.
• Cardiovascular secondary prevention: a meta-analysis of controlled trials after acute myocardial infarction found no additional benefit above 3 g/day.
• Glycaemic and lipid measures: doses above 1 g/day reduced fasting glucose and triglycerides and raised HDL in a dose-response meta-analysis.

Talenezhad 2020 meta-analysis of 37 randomised controlled trials with dose-response analysis for weight and body composition, Pooyandjoo 2016 and a 2019 updated dose-response meta-analysis for weight management in overweight adults, and a 2025 meta-analysis of L-carnitine monotherapy for idiopathic male infertility. The weight effect is consistent and small; the fertility evidence is the more clinically interesting.

1-3 g/day. The cardiovascular analysis found no marginal benefit above 3 g/day. Acetyl-L-carnitine is preferred where a central nervous system effect is wanted because it crosses the blood-brain barrier; L-carnitine L-tartrate is the usual sports format; propionyl-L-carnitine has the vascular literature.

GI upset, nausea and a fishy body odour at higher doses, the last from bacterial conversion in the gut. Well tolerated at 1-3 g/day.

Gut bacteria convert carnitine to trimethylamine, which the liver oxidises to TMAO, a metabolite associated with cardiovascular risk in observational work. The clinical significance for supplement users is unsettled and worth raising with a prescriber if you have cardiovascular disease. May potentiate warfarin. Thyroid hormone action can be reduced, so people on replacement should mention it.