Oral L-carnitine bioavailability ~10%
Oral L-carnitine has very low bioavailability of roughly 10%, requiring doses of 1,000–5,000 mg/day to achieve a therapeutic effect.
Snapshot · Huberman Lab
Essentials: Tools for Hormone Optimization in Males | Dr. Kyle Gillett
Explore episode
Jul 2, 2026
Where this was said
L-Carnitine, Forms, Dose, TMAO, Garlic & Berberine
At 16:40 · chapter starts 15:50
The L-carnitine discussion covers practical ground: injectable forms require a prescription and are absorbed intramuscularly, while oral forms have only about 10% bioavailability, necessitating daily doses of 1,000–5,000 mg for effect. Gillett then delivers L-carnitine's most surprising benefit — it increases the density of androgen receptors in the cell cytoplasm, meaning the body responds more powerfully to the same testosterone level. Tadalafil shares this receptor-density effect, he notes. At high doses, L-carnitine raises the risk of TMAO production from gut bacteria, a potential carcinogen. Gillett recommends allicin (from garlic, ~600 mg) taken alongside high-dose carnitine to reduce TMAO conversion. Berberine offers a similar protective effect but comes with its own side effects — blood sugar drops (including the 'dawn phenomenon' during sleep) and headaches, as Huberman personally confirms. Crucially, none of these supplements — creatine, betaine, or L-carnitine — require cycling.
L-carnitine increases androgen receptor density
L-carnitine increases the density of the androgen receptor in the cytoplasm of cells, amplifying testosterone's effect even without changing testosterone levels.
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