L-Carnitine
Transports fatty acids into mitochondria and supports testosterone receptor activity.
What is L-Carnitine?
Carnitine is a compound synthesised in the body from lysine and methionine, with red meat being the primary dietary source. It plays a central role in energy metabolism, transporting long-chain fatty acids into the mitochondria where they are burned for fuel. The acetylated form (ALCAR) also crosses the blood-brain barrier and has nootropic properties.
What does the evidence say?
A 2011 study by Kraemer et al. found L-carnitine L-tartrate supplementation at 2g per day significantly increased androgen receptor density in muscle tissue: effectively making available testosterone more active. A 2013 meta-analysis by Pooyandjoo et al. found modest but significant effects on body weight reduction. ALCAR research shows benefits for age-related cognitive decline and peripheral neuropathy (Di Marzio et al., 1992).
Good evidence from several studies, but with some limitations in size, duration, or methodology.
Dosage guide
| Effective dose | 1–3g per day of L-carnitine L-tartrate for performance; 500mg–2g of ALCAR for cognitive effects |
| Maximum dose | 4g per day (higher doses show no additional benefit) |
| Timing | With a carbohydrate-containing meal to maximise uptake via insulin-mediated transport. |
Best form to buy
L-carnitine L-tartrate (LCLT) for exercise performance and testosterone receptor research. Acetyl-L-carnitine (ALCAR) for brain and cognition. Standard L-carnitine is less bioavailable than either.
Who benefits most
Men who eat little or no red meat (vegetarians/vegans), men over 40 looking to support testosterone receptor sensitivity, and anyone interested in cognitive support alongside exercise.
Side effects and safety
Generally safe. High doses can cause a fishy body odour in some people due to bacterial conversion in the gut. Some research suggests carnitine may increase TMAO production, a cardiovascular risk marker: though this is debated and likely only relevant at very high doses.
“The testosterone receptor research is underrated. This isn't a testosterone booster in the traditional sense, but increasing receptor density means the testosterone you already produce works harder. Worth including if you're already on top of the basics.”