L-Carnitine

Supplements · Sports Performance · Supplement, Typed Supps

Shuttles fat into the part of your cells that burns it.

Stage by stage

Intake (Capsule or powder): Absorption is relatively limited and inconsistent between individuals.
Small intestine (Limited, inconsistent absorption): Absorption is relatively limited and can be inconsistent between individuals.
Bloodstream (Carried to muscle): Carried in the blood to tissues, especially muscle.
Muscle tissue (Transports fatty acids): Helps transport fatty acids into mitochondria, where they’re converted into energy.

Producing modest weight or fat loss — limited evidence. Meta-analyses show a small average reduction in body weight, mainly in adults with overweight or obesity; the effect is minor and inconsistent.
Reducing muscle soreness and markers of exercise damage during recovery — limited evidence. Some small trials suggest less soreness and lower damage markers, but studies are small and results mixed.
Acting as a fat-burning or performance aid in healthy, trained people — insufficient evidence. Despite the marketing, controlled trials do not show a reliable ergogenic or fat-oxidation benefit in people who are not deficient.
Evidence that it causes Raising TMAO, a cardiovascular risk marker — moderate evidence. Gut bacteria convert carnitine to TMA and then TMAO; supplementation raises plasma TMAO substantially and dose-dependently, and levels fall again after stopping.

1–3 g daily, commonly 2 g, in divided doses

Upper limit: No established UL; doses up to about 2–3 g/day are generally tolerated

With food, standard dosing.

Warfarin and other coumarin anticoagulants: Carnitine may enhance the anticoagulant effect, raising INR and bleeding risk. (moderate)
Thyroid hormone (levothyroxine): Carnitine can antagonise thyroid hormone action at the tissue level, potentially blunting treatment. (moderate)

“L-carnitine burns fat on its own.” In reality: Taking more doesn’t necessarily increase fat burning — most people already make enough naturally.