Injectable L-carnitine is an FDA-approved drug for carnitine deficiency. The only randomized injected weight-loss trial pepmg found lasted 7 days.

The approved drug

Levocarnitine injection: intravenous, 200 mg/mL, two uses

Levocarnitine (L-carnitine) is a carrier that moves long-chain fatty acids into mitochondria, where they are burned for energy.[1] FDA first approved Carnitor injection under NDA 020182 on December 16, 1992, as an orphan-drug submission.[3] On November 1, 2026, Drugs@FDA held 12 levocarnitine applications, tablets, oral solutions and five injections, and every injection was 200 mg/mL.[2]

The Carnitor injection label approves it for two things: acute and chronic treatment of an inborn error of metabolism that causes secondary carnitine deficiency, and prevention and treatment of carnitine deficiency in end stage renal disease patients on dialysis. It is labeled "For Intravenous Use Only," in 1 g per 5 mL single-dose vials with no preservative, and unused solution is to be discarded.[1] For dialysis patients, the label says, the effects of supplemental carnitine "on the signs and symptoms of carnitine deficiency and on clinical outcomes in this population have not been determined."[1]

The label gives oral bioavailability of about 15% for the tablets and solution. After a single intravenous dose, about 76% was excreted in the urine within 24 hours.[1] It warns of serious hypersensitivity reactions, including anaphylaxis, mostly in dialysis patients and some within minutes of an intravenous dose; lists seizures as a postmarketing report; and notes INR increases in people taking warfarin.[1]

The weight evidence

About a kilogram in supplement trials, with no clear change in body fat percentage

A 2016 meta-analysis of 9 randomized trials (911 people) found carnitine groups lost 1.33 kg more than controls (95% CI 0.57 to 2.09 kg), and that the difference shrank the longer people took it.[6] A 2020 meta-analysis of 37 trials (2,292 people) found 1.21 kg more weight loss and 2.08 kg less fat mass, but no significant effect on waist or body fat percentage; restricted to high-quality trials, only the weight effect held. Its dose-response analysis, expressed as daily ingestion, peaked at 2,000 mg a day.[7] A third 2020 meta-analysis of 43 trials found 1.13 kg, 1.16 kg less fat mass, no change in body fat percentage, an effect only in overweight and obese people, and no change in body measurements among hemodialysis patients.[8]

These are average differences against control groups, pooled across trials of different doses, forms and lengths. pepmg read the three meta-analyses as abstracts and did not count how many of their trials gave carnitine by injection.

Injected for weight

One 7-day randomized trial, during a fasting program

A Guangzhou group randomized 30 people with metabolic syndrome to a 7-day program (2 days of calorie restriction, then 5 days of modified fasting) with either 2 g of L-carnitine intravenously twice a day or saline. The trial was single-blind and called itself a pilot. The carnitine group lost 4.6 kg against 3.2 kg (P = 0.03 in the abstract, 0.04 in the results section) and 5.0 cm of waist against 1.7 cm, and reported less hunger and fatigue.[4] The authors listed the small sample and not measuring lean and fat mass as the two main limitations, and noted that hungrier control patients may have eaten more than allowed.[4]

The same group's 2019 look back at 192 fasting patients matched 40 who had carnitine infusions with 40 who had not. Weight fell 4.05 kg in the carnitine group against 3.25 kg (P = 0.031), but triglycerides and diastolic blood pressure fell more in the group without carnitine.[5] It was retrospective, not randomized.

pepmg's PubMed search for carnitine with injection or infusion terms and weight or body-composition terms in humans returned 19 records on November 1, 2026; these two fasting studies were the only weight-loss studies of injected carnitine pepmg found among them, and none of the records described carnitine given under the skin or into muscle.[17] ClinicalTrials.gov listed 10 studies with carnitine as an intervention and obesity as a condition that day, and none described an injected carnitine arm.[18]

Getting into muscle

Blood levels rose. Muscle levels needed insulin.

A Nottingham group noted in 2006 that earlier studies had failed to raise muscle carnitine in healthy people by diet or by intravenous carnitine. In 8 healthy men given a 5-hour intravenous L-carnitine infusion, muscle carnitine did not change when insulin stayed at fasting levels; when insulin was held high, it rose from 22.0 to 24.7 mmol per kg of dry muscle.[9] A second study by the group, in 7 men, found the same combination raised muscle carnitine by 15%, with signs of less carbohydrate use in muscle.[10]

The group then gave 14 healthy men either 80 g of carbohydrate or 2 g of L-carnitine L-tartrate with 80 g of carbohydrate, twice daily by mouth for 24 weeks, double-blind. Muscle carnitine rose 21% in the carnitine group, which used less muscle glycogen at low exercise intensity and increased work output 11% in a 30-minute cycling trial, while the control group did not change.[11]

Dialysis and TMAO

The approved population, and a route question

A 2022 Cochrane review of 52 randomized trials (3,398 people) in dialysis found L-carnitine may have little or no effect on fatigue, total quality of life or adverse events, and may improve the SF-36 mental score and slightly raise hemoglobin (0.46 g/dL), all at low certainty. It concluded the evidence "does not currently support" carnitine supplementation for dialysis-related carnitine deficiency.[12]

In a 2013 Nature Medicine study, gut bacterial metabolism of ingested L-carnitine produced TMAO; omnivores made more TMAO than vegans or vegetarians, and dietary L-carnitine increased atherosclerosis in mice unless their gut bacteria were suppressed. Among 2,595 people undergoing cardiac evaluation, plasma L-carnitine predicted cardiovascular risk only in those who also had high TMAO, an observational finding.[13] The injection label also warns that chronic high oral doses in people with severely compromised kidney function or on dialysis may let TMA and TMAO accumulate.[1] In a 2018 study of atherosclerosis-prone male mice on a high-fat diet, oral L-carnitine raised TMAO and plaque, while L-carnitine given under the skin did not.[14] That is a mouse result; pepmg found no human study comparing the routes.

Status and the market

A compounding route, a sport limit, higher listed concentrations

Under section 503A, a pharmacy may compound with a bulk substance that complies with a USP or NF monograph if one exists, is a component of an FDA-approved drug if none exists, or is on FDA's 503A bulks list.[15] Levocarnitine is the active ingredient of approved drugs.[2] pepmg did not check USP monograph status.

The World Anti-Doping Agency prohibits "Intravenous infusions and/or injections of more than a total of 100 mL per 12-hour period" except those legitimately received in hospital treatment, surgery or clinical diagnostic investigations. That rule covers any infusion, whatever it contains.[16]

In pepmg's index generated October 31, 2026, 33 of the 99 vendors with listings carried L-carnitine, 47 listings in all, 7 of them blends. Of the 17 listing names that state a concentration, all state 400 to 600 mg/mL.[19] pepmg makes no claim about what is in any vendor's product. The study doses above are reported as published, with their populations, not as guidance.

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