L-Carnitine

Last reviewed October 2026 · Based on 19 studies

Bottom line

L-carnitine supplements led to about 1.2 kg more weight loss than control in a meta-analysis of 37 randomized trials, mainly in people with overweight or obesity. In type 2 diabetes it modestly lowered HbA1c and LDL cholesterol, but trial results varied widely. In healthy people it raised blood TMAO, a compound thought to promote artery disease, and long-term heart effects are not known.

What it helps with

Helps you lose weight and body fat — Benefit, evidence grade B (Moderate). Meta-analyses of 37 and 43 randomised trials agree on a small effect (about 1 kg), seen in overweight and obese adults; downgraded once for moderate heterogeneity and effect shrinking over time.
Improves blood sugar control in type 2 diabetes — Benefit, evidence grade C (Limited). Meta-analyses of RCTs with very high heterogeneity (I2 about 94%); surrogate marker; small effect.
Lowers LDL cholesterol — Benefit, evidence grade C (Limited). Meta-analyses of RCTs mostly in diabetes with very high heterogeneity; surrogate marker.
Raises a blood marker linked to artery disease (TMAO) — Harm, evidence grade C (Limited). Systematic review of 11 studies in healthy people showing a rise in a biomarker; no clinical heart outcomes studied.

What it is

L-carnitine is a vitamin-like substance taken as a supplement [1].

What the research says

Weight and body fat. A 2020 meta-analysis of 37 randomized trials (2,292 people) found L-carnitine lowered body weight by 1.21 kg (95% CI 0.68 to 1.73), BMI by 0.24 kg/m2 and fat mass by 2.08 kg, with no significant effect on waist circumference or body fat percentage; analysis of high-quality trials only confirmed the weight effect [1]. A 2020 update of 43 trials found weight down 1.13 kg (0.67 to 1.59), BMI down 0.36 and fat mass down 1.16 kg, but only in overweight and obese adults and not in people on hemodialysis; weight and BMI results were reported for L-carnitine combined with other lifestyle modifications [2]. A 2016 meta-analysis of 9 trials (911 people) found 1.33 kg more weight lost, with the effect decreasing over longer durations [3].

Type 2 diabetes. A 2024 meta-analysis of 21 randomized trials (2,041 people) found each 1 g a day lowered BMI by 0.37 kg/m2 (low certainty), HbA1c by 0.16 percentage points (moderate certainty) and LDL cholesterol by 0.11 mmol/L (high certainty), with high statistical heterogeneity (I2 91 to 94%), so results should be read cautiously [4]. Another meta-analysis of 21 trials (2,900 people with impaired glucose tolerance or diabetes) found lower LDL (-12.66 mg/dL), fasting glucose, HbA1c (-0.37%), weight (-1.58 kg) and C-reactive protein [5]. A meta-analysis of 15 trials in adults found lower fasting glucose (-4.94 mg/dL), insulin resistance, triglycerides, total cholesterol, LDL (-8.28 mg/dL) and ALT, with no significant change in HDL [6].

Blood marker linked to artery disease. A systematic review of 11 studies in healthy people taking 1 to 4 g a day for 12 or 24 weeks found L-carnitine raised fasting plasma TMAO, a compound thought to promote artery disease, without changes in inflammatory or oxidative stress markers [7]. The review also found that 24 weeks of L-carnitine did not affect muscle strength in healthy older women [7].

Doses used in studies

The weight dose-response analysis suggested 2,000 mg a day gave the largest effect on body weight in adults [1]. In type 2 diabetes, effects were modelled per 1 g a day, with lipid and glucose reductions continuing up to 4 g a day [4]. Trials in healthy people used 1 to 4 g a day for 12 to 24 weeks [7].

Safety and interactions

Common side effects. The meta-analyses reviewed did not report common side effects in their abstracts, so no data were found here.

Upper limits and toxic doses. No upper intake limit was established in the studies reviewed. Trials used up to 4 g a day [7][4].

Interactions. In one case report, 1 g a day of carnitine reversed raised blood ammonia in a woman taking valproic acid for epilepsy; this is evidence from a single patient [8]. No other interaction data were found in the studies reviewed.

Pregnancy and breastfeeding. No data were found in the studies reviewed.

Relevant conditions. L-carnitine raised blood TMAO in healthy people, and the authors called for studies of long-term cardiovascular effects [7]. In people on hemodialysis, weight and BMI did not change [2].

Caveats and open questions

The weight effect is small (about 1 kg), tends to shrink over time and appears only in overweight and obese adults [1][3][2]. Diabetes trials had very high heterogeneity [4]. Long-term cardiovascular effects, including those linked to TMAO, have not been tested [7].