L-Carnitine

What it is

L-carnitine is not a peptide. It is a small compound made from the amino acids lysine and methionine, and found in red meat and dairy. Your liver and kidneys make it too. It carries fatty acids into the mitochondria, the parts of your cells that burn them for energy.

Levocarnitine injection is a licensed prescription medicine for people with carnitine deficiency, including some dialysis patients. In fitness circles, it is promoted as a fat burner, and research-chemical sellers supply it as a ready-made liquid for injection.

The logic sounds neat (more carnitine, more fat burned) but in people with normal levels, the evidence for fat loss is modest at best.

History

Carnitine was discovered in muscle tissue in 1905, and its role in fat metabolism was worked out in the 1950s. Deficiency syndromes were described in the 1970s, which led to its use as a medicine. It became a popular supplement from the 1980s.

How it works

Long-chain fatty acids need carnitine to cross into the mitochondria for oxidation. If you are deficient, fat burning is impaired. If you are not, extra carnitine does not necessarily increase it, as the transport system is already working, and muscle carnitine is hard to raise with supplements alone. Raising muscle levels may need long-term supplementation combined with insulin from carbohydrates, according to some studies.

Dosage

• Licensed use is for deficiency and dialysis, at doses set by a clinician (typically 10-20 mg/kg by IV after dialysis, in the licensed product).
• For fat loss or exercise, oral doses of 1-3 g a day have been studied. Injectable doses used in fitness circles are commonly reported at 300-1,000 mg, a few times a week, but this is anecdotal.
• More is not necessarily better, and the evidence for injections over oral is lacking.
• A 600 mg per 10 ml vial gives 60 mg per ml. A 1 ml dose is 60 mg, so a 600 mg dose is the whole vial, which is a large volume for one injection.

How it is taken

• Intramuscular or subcutaneous injection using a standard needle. Volume matters: 5 ml or more is painful and is better split across sites.
• Oral L-carnitine and acetyl-L-carnitine are better-studied and far easier to use than injectables.

How to reconstitute

• This product is already a liquid: there is nothing to reconstitute. A 600 mg per 10 ml vial is 60 mg/ml.
• On a 1 ml insulin syringe, that is 0.6 mg per unit, so 100 units (1 ml) is 60 mg, 5 units is 3 mg. A 300 mg dose is 5 ml, which is too big for a 1 ml syringe, so you would need a larger syringe.
• Check the label to see the solvent and whether it contains preservatives, and discard if the solution is not clear.

How it should arrive

Sealed glass vial of clear, colourless liquid with an intact rubber stopper and crimped cap. Check that the label states concentration and batch.

How it should look once reconstituted

Clear and colourless, with no particles. Cloudiness, colour change or floating specks mean do not use it.

What to expect, and when

• In people who are deficient, energy and muscle weakness can improve within weeks.
• For fat loss, trials of oral carnitine show small effects over 8-12 weeks or more.
• Do not expect noticeable fat loss without diet and exercise changes.

Side effects

• Nausea, vomiting, stomach cramps and diarrhoea, particularly at higher doses.
• A fishy body odour, caused by trimethylamine.
• Injection-site pain or burning.
• Seizures have been reported in people with seizure disorders.
• Muscle weakness in some people with kidney disease.

Risks

• Gut bacteria turn carnitine into TMAO, a compound that has been linked with heart disease in observational studies. Whether supplements raise heart risk is unresolved, but long-term high doses are a reason for caution if you have heart disease.
• It can interact with blood thinners (warfarin) and thyroid medication, and is not recommended with an underactive thyroid unless guided by a doctor.
• Caution with epilepsy, kidney disease, and in pregnancy or breastfeeding unless advised.
• Non-prescribed injection means unlicensed product with uncertain sterility and potency.
• Meta-analyses of oral L-carnitine show modest weight loss on average (on the order of a kilogram or so over several weeks), which is small and of uncertain importance.

Potential gains

• Treating true carnitine deficiency, including in some dialysis patients, which is well established.
• A small average weight-loss effect in pooled studies of oral carnitine.
• Possible modest reductions in muscle soreness and improved recovery after exercise in some trials.
• No solid evidence that injections burn more fat than a good diet and training.

Other useful information

If fat loss is the goal, diet quality, calories and resistance training do far more than any carnitine product. If you do want to try carnitine, the oral form is cheaper, easier and has most of the research behind it.