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Carnitine (β-hydroxy-γ-trimethylaminobutyric acid) is a quaternary amine synthesized from lysine and methionine. It transports activated long-chain fatty acids across the inner mitochondrial membrane via the carnitine palmitoyltransferase (CPT) system. Without carnitine, fatty acids cannot enter mitochondria for β-oxidation.
Forms:
Carnitine may potentiate warfarin — case reports of increased INR
Carnitine may inhibit thyroid hormone entry into cell nuclei; high doses interfere with thyroid function
Valproic acid depletes carnitine; supplementation may be recommended
Gut bacteria metabolize carnitine to trimethylamine (TMA), which the liver converts to TMAO. Elevated TMAO is associated with increased cardiovascular risk in observational studies (PMID: 23563705). However: (1) this is associational, not causal; (2) fish contains more TMAO precursors than carnitine supplements; (3) the post-MI meta-analysis showed carnitine REDUCED cardiovascular events despite TMAO. The concern is noted but not definitive.
Not Prohibited
DiNicolantonio JJ et al. L-carnitine in the secondary prevention of cardiovascular disease: systematic review and meta-analysis.
Koeth RA et al. Intestinal microbiota metabolism of L-carnitine, a nutrient in red meat, promotes atherosclerosis.
Wall BT et al. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content.
Cavallini G et al. Carnitine vs androgen administration in treatment of sexual dysfunction.
Independently graded against 173,636 indexed supplements with 177 published clinical interactions, sourced from PubMed, FDA CAERS, openFDA, and NIH DSLD | Last updated: April 2026
Not medical advice. Based on published clinical research and systematic reviews.