L carnitine supplements can cause a fishy odor in the breath, sweat, and urine. This is likely due to the formation of trimethylamine (TMA). TMA is also responsible for the pungent smell of Pharmacokinetics of L Carnitine : Clinical Pharmacokinetics Trimethylaminuria: Understanding and Treating Fish Odor Syndrome L Carnitine Linus Pauling Institute Oregon State University L Carnitine in the Treatment of Psychiatric and Neurological Manifestations: A Systematic Review Comparison of short term and long term effects of peroral L carnitine intake: clinical implications of elevated TMAO levels in cardiovascular complications