Some studies report a “fishy” odor emanating from breath and sweat following supplementation with L-carnitine, which is likely due to the formation of trimethylamine.[1] Dry mouth and gastrointestinal discomfort have also been reported in some studies using L-carnitine,[2] while gastrointestinal problems (including nausea and gastric pain) are a common adverse effect of propionyl-L-carnitine.[3][4] However, several meta-analyses conclude that L-carnitine and its derivatives are generally safe and well‐tolerated.[5][3][4] Furthermore, supplementation of up to 2000 milligrams (mg) per day is considered safe for human consumption.[6] Some human studies have even used doses of L-carnitine as high as 6000 mg/day without serious side effects,[7] but a thorough safety evaluation of such high doses is lacking.[6]
