L-Carnitine

Carnitine · Levocarnitine

Snapshot

Indications	Contraindications
Primary carnitine deficiency¹ Dialysis-related anemia² Insulin resistance^{3, 4} Glycemic markers³ Weight loss⁵ Male infertility sperm motility⁶ Valproate toxicity adjunct⁷	Seizure disorder⁸ Pregnancy or breastfeeding⁸

Carnitine is a conditionally essential nutrient made in the liver, kidneys, and brain from lysine and methionine, and supplied by red meat and other animal foods⁹. It carries long-chain fatty acids into mitochondria for energy production⁹. Supplementation follows from that role: correcting primary and secondary deficiency, including in dialysis, and metabolic uses such as insulin resistance, weight loss, and male fertility. It is also taken for exercise performance and recovery, where results are mixed¹⁰. Patients on a vegan diet or with kidney or liver disease are most prone to low status.

The evidence is split. In male infertility it improved sperm motility and morphology, without evidence of more pregnancies⁶. In 2025, a pharmacokinetic study in healthy volunteers found most of an oral dose was converted to trimethylamine-N-oxide (TMAO), a compound linked to adverse cardiovascular outcomes; no outcome trial has tested the consequence. Supplements are sold mainly as L-carnitine and acetyl-L-carnitine; see Form comparison.

The most consequential caution is cardiovascular: gut bacteria convert carnitine to TMAO, and supplementation raised fasting TMAO in healthy adults¹¹.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

89 sources, 72 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources