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L-Carnitine

L-Carnitine and ALCAR are two related compounds used for a variety of purposes, including boosting exercise performance and improving cognition and depression. L-Carnitine is often used for fat loss, but evidence doesn't support this indication.

Our evidence-based analysis on l-carnitine features 272 unique references to scientific papers.

Research analysis led by Kamal Patel .
Reviewed by
Examine.com Team
Last Updated:

Summary of L-Carnitine

Primary Information, Benefits, Effects, and Important Facts

What is L-Carnitine?

L-Carnitine is a compound produced by the body from lysine and methionine. It can be acetylated to produce Acetyl-L-Carnitine (ALCAR), which is similar but crosses the blood-brain barrier more efficiently. L-Carnitine is best known for its involvement in the mitochondrial oxidation of long-chain fatty acids.

It's found in food and is most prevalent in meat, and beef in particular.

What are L-Carnitine's benefits?

A notable improvement in sperm quality has been found with supplementation of high doses. It may modestly reduce fatigue in elderly people with low muscular endurance but its effects on athletes during physical activity aren't well-supported. L-Carnitine may slightly limit muscle damage during resistance exercise. Minor beneficial effects on blood glucose and insulin sensitivity have been noted in people with diabetes and healthy people alike, but much more research is needed to confirm this.

When it comes to fat-burning, studies on ALCAR in isolation do not show very good results. Some studies have found minor fat loss, which is typically attributed to increased physical activity due to increased energy levels.

What are L-Carnitine's side effects and downsides?

A few studies have noted a benign adverse effect of 'odd smell', which is said to be due to the formation of trimethylamines; it has occurred at a frequency of 4%.

Does L-carnitine help with weight loss?

Probably only if it helps to reduce fatigue and that leads to an increase in physical activity. It's possible that very low carnitine levels could lead to impaired fatty acid oxidation, but for most people, there isn't a notable increase in resting fatty acid oxidation when taking L-carnitine.

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How to Take L-Carnitine

Recommended dosage, active amounts, other details

The standard dose for L-carnitine is between 500-2,000mg.

There are various forms of carnitine supplementation available. Acetyl-L-Carnitine (ALCAR) is used for cognitive enhancement. L-Carnitine L-Tartrate (LCLT) is typically used for physical performance and power output. Glycine Propionyl L-Carnitine (GPLC) is used to alleviate intermittent claudication and blood flow issues.

L-carnitine is supplemented daily.

The equivalent dosage range for other forms of L-carnitine are as follows: 630-2,500mg (ALCAR), 1,000-4,000mg (LCLT) and 1,000-4,000mg (GPLC).

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Human Effect Matrix

The Human Effect Matrix looks at human studies (it excludes animal and in vitro studies) to tell you what effects l-carnitine has on your body, and how strong these effects are.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
Notes
grade-b Notable Very High See all 4 studies
A decrease in ammonia has been noted, and appears to influence both hepatic encephalopathy as well as persons with no significant liver damage
grade-b Notable High See all 5 studies
Carnitine at 3g daily appears to increase sperm quality mostly related to sperm morphology; there are mixed effects on sperm motility
grade-b Notable Very High See all 3 studies
Symptoms of intermittent claudation are notably reduced with L-Carnitine supplementation (the rate of improvement over time, as assessed by walking distance, seems to be doubled; ie. from 40% to 60% or 60% to 90%) and associated with the Propinyl-L-Carnitine form (found in the supplement GPLC). The role of propinoic acid cannot be ruled out at this time, and studies have note used basic L-carnitine or ALCAR
grade-b Minor Very High See all 3 studies
A decrease in blood glucose has been noted with carnitine supplementation
grade-b Minor Very High See all 5 studies
A decrease in the exercise-induced increase in MDA levels is seen with carnitine supplementation, possibly secondary to reducing damage to muscle tissue. The degree of MDA reduction is not overly remarkable
grade-b Minor High See all 3 studies
There appears to be a fat reducing effect of L-Carnitine supplementation, but this may be limited to elderly persons; limited studies in otherwise healthy youth and adults fail to note an effect
grade-b Minor High See all 7 studies
Carnitine appears to be somewhat effective in reducing fatigue in elderly persons with low muscular endurance and perhaps in chronic fatigue syndrome; there is insufficient evidence to support a role of carnitine in reducing exercise-induced fatigue
grade-b Minor High See all 4 studies
An increase in insulin sensitivity appears to exist with carnitine supplementation, and at least once has been noted in otherwise healthy lean males. This may be secondary to glucose disposition into tissues
grade-b Minor Moderate See all 5 studies
Lactate production appears to be decreased in studies that note an increase in muscular carnitine stores, although the decrease is not overly notable
grade-b Minor Very High See all 3 studies
The reduction in MDA that occurs during exercise may also occur at rest, suggesting a per se effect
grade-b Minor Low See all 3 studies
Unreliable and mixed effects, but some studies do note that muscular carnitine levels can be increased with carnitine supplements.
grade-b Minor Very High See all 4 studies
Biomarkers of muscle damage including creatine kinase and muscle soreness are both fairly reliably reduced following ingestion of carnitine and pairing with exercise
grade-b Minor Very High See all 4 studies
Cognitive side effects of hepatic encepalopathy are alleviated with carnitine supplementation, notably fatigue and cognitive performance.
grade-b - Moderate See all 5 studies
More evidence than not suggest no significant influence on low intensity and high duration cardiovascular exercise
grade-b - - See study
grade-b - High See all 3 studies
Rates of fat oxidation appear unaffected following carnitine supplementation
grade-b - Very High See 2 studies
No significant changes in HDL cholesterol seen with supplementation
grade-b - - See 2 studies
grade-b - - See study
grade-b - - See 2 studies
No detectable influence on LDL-C levels
grade-b - Moderate See all 5 studies
Highly mixed effects on power output, with mostly no significant influence but a possible increase in mean power output occurring in short-term anaerobic endurance exercise secondary to reducing the rate of perceived exertion
grade-b - - See study
grade-b - Very High See all 4 studies
For the most part, there does not appear to be a significant influence of carnitine on total cholesterol levels
grade-b - Very High See 2 studies
No significant influence on triglycerides
grade-c Notable - See study
High dose carnitine (50mg per kilogram) appears to reduce some symptoms of autism as assessed by rating scales; notable due to the rarity of a supplement towards this goal
grade-c Minor Very High See 2 studies
At least one study has noted reduction in ADHD symptoms in children
grade-c Minor - See study
An increase in adiponectin has been noted
grade-c Minor - See study
Secondary to reducing symptoms of ADHD, L-carnitine may reduce aggression in children.
grade-c Minor - See study
A reduced rate of relapse and alcohol cravings was noted with ALCAR ingestion relative to placebo
grade-c Minor Very High See 2 studies
An increase in anaerobic cardiovascular exercise has been noted with carnitine ingestion
grade-c Minor - See study
At least one study has noted an increase in androgen receptor density in skeletal muscle tissue
grade-c Minor Very High See 2 studies
An increase in all three main enzymes (SOD, glutathione peroxidase, catalase) has been detected following ingestion of carnitine
grade-c Minor Very High See 2 studies
An increase in attention has been noted to be secondary to reductions in the symptoms of chronic fatigue
grade-c Minor - See study
Increases in blood flow appear to occur following carnitine supplementation, which may be related to the increases in nitrate
grade-c Minor - See study
May reduce blood pressure
grade-c Minor Very High See 2 studies
Improvements in general cognitive capacity has been noted in elderly persons and in disease models (hepatic encepalopathy); lack of literature on otherwise healthy youth
grade-c Minor Moderate See 2 studies
A decrease in heart rate has been noted associated with supplementation
grade-c Minor - See study
An increase in IGF binding protein (3) has been noted following carnitine supplementation in otherwise healthy youth
grade-c Minor - See study
Possible antiinflammatory effect on exercise-induced inflammatory biomarkers
grade-c Minor - See study
Fasting insulin has been noted to be decreased in diabetics given carnitine
grade-c Minor Very High See 2 studies
An increase in lean mass has been noted in elderly persons. This may not apply to lean healthy individuals, and no research assesses youth
grade-c Minor - See study
A decrease in liver enzymes has been noted in a model of hepatic encepalopathy, a per se reducing effect is uncertain
grade-c Minor - See study
A decrease in muscle oxygenation has been noted during occlusion, but not during squat exercise; practical significance of these results unknown
grade-c Minor Very High See 2 studies
The decrease in muscle soreness appears to correlate with the reduced muscle damage
grade-c Minor - See study
An increase in nitric oxide has been noted, thought to be secondary to increases in plasma nitrate
grade-c Minor Very High See 2 studies
Plasma nitrate appears to be increased following carnitine ingestion, although not to the same degree as nitrate supplementation itself
grade-c Minor - See study
A reduction in the rate of perceived exertion appears to exist following carnitine supplementation
grade-c Minor - See study
Fibromyalgic symptoms are reduced with carnitine ingestion
grade-c Minor - See study
Some symptoms of hyperthyroidism are reduced following carnitine supplementation
grade-c Minor - See study
Some symptoms associated with multiple sclerosis are noted to be reduced with carnitine ingestion.
grade-c Minor - See study
A decrease in uric acid has been noted
grade-c - - See study
No significant changes in IGF-1 seen with carnitine supplementation; IGF-2 also appears unaffected
grade-c - - See study
No significant influence on metabolic rate noted with carnitine supplementation
grade-c - Very High See all 3 studies
No significant changes in subjective well being associated with carnitine intake
grade-c - - See study
No significant influence on TNF-a
grade-c - - See study
No significant alterations noted
grade-c - - See study
No detectable influence on VO2 max associated with carnitine supplementation
grade-d Minor - See study
One study has noted an improvement in erections in persons thought to have impaired blood flow
grade-d Minor - See study
Reduction in general oxidation seems to be secondary to antioxidant enzyme induction
grade-d - - See study

Frequently Asked Questions about L-Carnitine

What beneficial compounds are primarily found in animal products?

Things To Know & Note

Is a Form Of

Primary Function:

Also Known As

Acetyl-L-Carnitine, ALCAR, Acetylcarnitine, L-Carnitine-L-Tartrate, LCLT, Glycine Propionyl-L-Carnitine, GPLC, Levocarnitine, Levacecarnine, L-3-hydroxytrimethylamminobutanoate, carnitine

Do Not Confuse With

Carnosine (the product of beta-alanine)

Goes Well With

  • L-Carnitine, in the form of ALCAR, is anecdotally reported as a stimulant, but effects are less than of other known stimulants (such as caffeine). It is currently not known why these effects occur

  • There are four common forms of carnitine supplements: L-Carnitine, Acetyl-L-carnitine (ALCAR), L-Carnitine L-Tartrate (LCLT) and Propionyl-L-Carnitine (usually bound to Glycine and called GPLC)

  • At least one study has noted, in regards to nitric oxide increases, there to be non-responders to carnitine supplementation.[1]

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Research Breakdown on L-Carnitine

Click here to see all 272 references.