Metabolic and GLP-1

L-Carnitine, injectable

The route with the muscle evidence is the swallowed one

7 sections

Top of article
What it actually is
What it is supposed to do
What people take it for
The dose question
How to check you have the right molecule
What people get wrong
What is known about harm

What circulates: 250 to 1,000 mg into muscle, or a drip with no stated dose
What was studied: 4 grams a day, into a vein
The gap: Convention runs below the studied dose
How long it lasts: The entry gives no figure for how long levocarnitine lasts in the body, and I could not find one in the sources behind it.

What it actually is

Carnitine is a small molecule your body builds for itself out of two of the building blocks of protein, and also takes in from red meat. Levocarnitine is the L form of it. It is not a peptide, and it sits on peptide shelves because that is where injectables get sold. The injected version is a real approved prescription medicine with a real label, which almost nothing else on this site is: CARNITOR, 1 gram in a 5 millilitre vial, approved in December 1992, for use in a vein only. What the label covers is an inherited metabolic disease, and carnitine shortage in people whose dialysis machine strips it out of their blood. Fat loss and energy are not on it.

What it is supposed to do

The claim is that carnitine ferries long chain fats across the inner wall of the mitochondrion, the compartment inside a cell where fuel gets burned. For that to do anything, the carnitine has to get inside muscle cells, and it does not drift in. A pump called OCTN2 has to haul it uphill, because muscle already holds far more carnitine than blood does. So raising the level in the blood does not obviously change what the pump does, and when researchers measured it directly by taking muscle samples, five hours of infusion moved it by nothing unless insulin was also held artificially high by a second drip.

What people take it for

People run the drip and the compounded shot for fat loss and for energy. That is what the clinics sell it for, and neither is on the label. I found no randomised trial of it into a vein in an otherwise healthy adult eating normally, for fat loss or for performance.

The dose question

What circulates: 250 to 1,000 mg into muscle, or a drip with no stated dose
What was studied: 4 grams a day, into a vein; Zhang 2014, 30 patients with metabolic syndrome, inside a five day modified fast

Below the studied dose

The numbers that circulate sit below every injected dose in the published trial record, and they are also a different route: the vendor figures go into muscle, and every injected dose in that trial record went into a vein. At the top of the range they run into the label's own dialysis dose, which is 700 to 1,400 mg per session in a 70 kilogram adult. Neither clinic page in the entry publishes a milligram figure at all, and one low-quality vendor-facing aggregator states that no peer reviewed randomised trials evaluate that range, attributing it to protocols passed around on forums. What the numbers do line up with is the syringe. The compounded product is 500 mg per millilitre, so 250, 500 and 1,000 mg are half a millilitre, one and two, which the entry reads as packaging and labels inference rather than derivation.

Reported because it is what people use. Nothing here recommends any amount.

How long it lasts

The entry gives no figure for how long levocarnitine lasts in the body, and I could not find one in the sources behind it.

Route studied

Into a vein. Five hour infusions in healthy men, a 12 hour infusion in septic shock, a slow push into the return line after each dialysis session, and 4 grams a day during a supervised fast. The weight loss pooling was swallowed, and so was the one protocol I found that raised muscle carnitine outside a laboratory insulin clamp. Five hours into a vein did raise it, but only while insulin was held high by a second drip.

Route used

A drip into a vein at a clinic, weekly or fortnightly, and a compounded shot into muscle.

How to check you have the right molecule

Read the strength on the vial, because it tells you which of three products you are holding. The approved injection is 1 gram in a 5 millilitre vial, 200 milligrams per millilitre, and says on its face that it is for use in a vein only. The compounded version sold to clinics is 500 milligrams per millilitre in a 30 millilitre vial, two and a half times the approved concentration, prepared under section 503A, and its own page carries the line that safety and effectiveness for that formulation have not been evaluated by the FDA. The molecule itself is levocarnitine, the L form, PubChem number 10917.

Walked through on two real certificates in how to read a certificate of analysis.

What people get wrong

The pitch is that injecting skips the gut, and that part is true, since only about 15 percent of a swallowed dose reaches the blood. The gut is not where the shortfall is. Muscle already holds far more carnitine than blood, so getting more in means pushing it uphill through a pump, and five hours of infusion at roughly ten times the blood carnitine the label calls normal moved muscle carnitine by nothing unless insulin was also pinned high by a second drip, which is a laboratory procedure and not something a clinic does. The only protocol I found that raised it outside that setup was swallowed: 24 weeks of 4 grams a day taken with 160 grams of sugar a day.

What is known about harm

The label's one serious warning is an allergic reaction: anaphylaxis, swelling of the voice box and spasm of the airways, reported mostly in dialysis patients and sometimes within minutes of a dose into a vein. Seizures have been reported by either route, in people with and without a history of them. On overdose the label reports no cases of toxicity in people and warns that large doses may cause diarrhoea, and its only numbers there are in rodents: 5.4 grams per kilogram into a vein kills half of rats, and 19.2 grams per kilogram swallowed kills half of mice.

Others in Metabolic and GLP-1

Everything on this page is a summary. The citations, the studies and the reasoning live in the full entry.

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