L-Carnitine: Usage, Health Benefits, and Side Effects

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L-carnitine is a naturally occurring chemical compound in the body with a structure similar to that of amino acids. Our bodies can produce enough L-carnitine on their own, but it is also available in supplement form.

The primary function of L-carnitine in the body is energy production. This explains why it is quite popular as a supplement for people in the fitness arena.

Apart from enhancing performance and stamina for athletes and fitness enthusiasts, L-carnitine is also popular for other health benefits, including improving heart health and brain function.

This article delves into the current scientific research on L-carnitine’s purported effects on various health conditions. We also look at L-carnitine functions in the body, potential side effects, dosing considerations, risk factors, and safety.

What is L-carnitine?

L-carnitine is a conditionally essential amino acid derivative chemical compound that naturally occurs in our bodies.

Being a conditionally essential nutrient means that the body produces enough L-carnitine even without dietary intervention except in unique circumstances. These unique circumstances are primary L-carnitine deficiency and secondary L-carnitine deficiency.

Primary L-carnitine deficiency is a genetic disorder that inhibits the carnitine transporter system’s normal functioning, limiting the compound’s availability. It is more prevalent among pre-term babies and manifests in skeletal muscle weakness and cardiomyopathy by age five (1).

Secondary l-carnitine deficiency, on the other hand, is characterized by low carnitine levels in blood plasma. It stems from many health problems, including; kidney disease, intestinal issues, mitochondrial disease, and certain medications (2).

L-carnitine is synthesized by the amino acids L-lysine and L-methionine in the liver, kidneys, and skeletal muscle (3). It is also stored in these organs for future use.

L-carnitine is necessary for energy production in the body. It transports long-chain fatty acids to the mitochondria, the cell site where fatty acids are oxidized to produce energy (4).

L-carnitine is also used in the transportation of toxic waste from the oxidation process away from the cell. Since L-carnitine is essential for energy production, it is also vital for all metabolism and physiological processes that require energy.

Although healthy individuals synthesize ample L-carnitine amounts, you can still acquire trace amounts of L-carnitine through diet. L-carnitine’s primary dietary sources are animal proteins like meat, fish, chicken, pork, and milk (5).

Red meat is a richer source of L-carnitine than white meat. L-carnitine is also available in supplement form.

Dietary L-carnitine is absorbed in the small intestines.

L-Carnitine Health Benefits
L-Carnitine Health Benefits

Is L-carnitine Safe?

Most studies on L-carnitine show that it is relatively safe to take and has no adverse side effects. It is also well-tolerated in both dietary and supplement forms by most people.

The Food and Drug Administration (FDA) has approved L-carnitine in both oral and IV forms to treat L-carnitine deficiency (6).

However, the safety of L-carnitine supplements varies from product to product.

Despite L-carnitine being considered generally safe, some users may exhibit mild symptoms.

Some studies also show that long-term use of L-carnitine may raise trimethylamine-N-oxide (TMAO) levels. Elevated TMAO levels are a risk factor for atherosclerosis, a cardiovascular disease that hardens the arteries (7).

Anyone intending to take L-carnitine supplements should consult their doctor first.

L-carnitine Health Benefits

L-carnitine is quite popular as a therapeutic agent for a range of health conditions. Note, however, that popular belief does not always qualify as truth.

Below, we look at some of L-carnitine’s popular health benefits and test them against scientific evidence.

1. Aids with weight loss

L-carnitine is a popular ingredient in fat burner supplements because of the belief that it has thermogenic properties.

What science says

Scientific studies on the effects of L-carnitine supplementation have been conducted on animals and in clinical trials.

One such study was conducted on rat subjects to establish L-carnitine’s effects on weight loss and body composition. The placebo-controlled study included two groups of rats, with each rat having an initial body weight of 460g.

Both groups of rats were fed on an energy-deficient diet, but the diet in one group was treated with L-carnitine. The experiment lasted 23 days.

At the end of the study, the rats that were treated with L-carnitine showed significant weight loss. They also showed a shift in body composition with more protein compared to fat.

However, there was no difference between the treated and the control group of rats on clinical parameters of weight loss. These include blood plasma levels of glucose, triglyceride, cholesterol, and fatty acids.

The study concluded that L-carnitine has no significant clinical effect on weight loss (8).

Another study was conducted on the effects of thermogenic fat loss supplements, including L-carnitine, on the resting metabolic rate. The resting metabolic rate (RMR) is the total amount of calories burned when resting.

A raised RMR is a selling point for fat burner supplements as it is believed to hasten weight loss. The study recommended further research to establish whether an elevated RMR led to a reduced fat mass (9).

A meta-analysis was conducted on the effects of L-carnitine on weight loss among obese and overweight subjects. It showed that L-carnitine could cause weight loss among overweight people combined with lifestyle modifications like exercise and diet (10).

We can, therefore, say that the effect of L-carnitine on weight loss remains mostly inconclusive.

2. Improves exercise performance

L-carnitine is believed to improve stamina during exercise and recovery time after exercising.

What science says

Various studies have been conducted on the use of L-carnitine as an ergogenic aid. Ergogenic aids are substances that improve strength and endurance, giving athletes a competitive advantage.

A placebo-controlled study was conducted among health athletes to establish the effect of L-carnitine on various exercise factors. These were exercise performance, anaerobic capacity, and oxidative stress.

The study was conducted among male athletes undergoing resistance training over nine weeks.  The participants were monitored and tested for various markers taken on the third week, the sixth week, and the 9th week.

There was a significant increase in the capacity to do specific exercises. The tests also recorded a decrease in lactic acid concentration in the blood post-exercise.

Lactic acid is what causes those painful cramps after exercising. The results also showed a reduction in post-exercise oxidative stress.

This study showed that L-carnitine could improve exercise performance while inhibiting lactic acid and oxidation levels (11).

However, several research reviews were conducted on online research databases with publications on the effect of l-carnitine on exercise. The reviews concluded that studies into the use of L-carnitine supplementation for exercise remain quite vague (12) (13).

Both reviews recommended that more studies need to be conducted on the effects of L-carnitine supplementation on exercise.

3. Delays the onset of degenerative brain diseases

L-carnitine is believed to improve brain function by enhancing learning markers and slowing down age-related mental decline.

What science says

Several research studies have been conducted on the neuroprotection properties of L-carnitine. Neurotherapy is the ability of a substance or therapy to prevent cell dysfunction and eventual death of brain cells (14).

Most research studies on L-carnitine’s effect on the brain are based on its modified form known as Acetyl L-carnitine (ALCAR).

A study was conducted on the effects of ALCAR on memory, learning capacity, and synaptic functions of aged rats. Synaptic function is the communication of neurons (brain cells) with target cells and organs across a synapse (where impulses pass).

One group of rats was given 100mg of L-carnitine/kg of body weight for three months, while the other got a placebo. During this period, they were submitted to specialized tasks that evaluated their learning capacity.

At the end of the study, the rats given ACLAR showed increased synaptic transmission in the brain (15). ACLAR is, therefore, beneficial for the brain function of aged mammals.

Based on the above evidence, clinical studies were conducted on dementia and Alzheimer’s disease (16) (17). The clinical studies concluded that more research needs to be performed on larger groups over a longer period for conclusive results.

4. Improves depression symptoms

L-carnitine is also believed to be a beneficial therapy agent for patients with depression.

What science says

Various research studies posit that depression is more prevalent among people with low L-carnitine plasma levels in the blood (18). Clinical studies have also been conducted to establish the effects of L-carnitine on depression.

Two meta-analyses were conducted on the effects of L-carnitine on depression. The meta-analyses were performed on randomized controlled tests (RCTs) involving L-carnitine, whose findings were published in various research databases.

Both meta-analyses showed that L-carnitine has great potential as a therapeutic option for depression. The most outstanding results were realized from trials that included aged subjects (19) (20).

While the mechanism of action remains unknown, L-carnitine remains a viable option for the treatment of depression.

5. Improves heart health

L-carnitine is believed to lower the risk of cardiovascular disease by regulating risk factors for cardiovascular disease. These include blood pressure and diabetes.

What science says

Research into the effects of L-carnitine on cardiovascular health shows that L-carnitine effectively reduces the risk factors for heart disease (21). The results echoed among different age brackets, from pre-teens to aged adults.

Despite L-carnitine’s notable positive effect on cardiovascular health, more clinical trials need to be conducted.

6. Slows down aging

L-carnitine is believed to slow down the process of aging.

What science says

Studies were conducted into the effects of L-carnitine on aging. The studies, which were placebo-controlled, revealed that l-carnitine reduced the byproducts of oxidation (22).

Free radicals released into the oxidation process are the leading cause of accelerated aging and other medical conditions. The mechanism of action by which L-carnitine slows down aging involves removing free radicals from the mitochondria.

L-carnitine prevents these free radicals from bonding with and destroying healthy cells.

Other research studies show that L-carnitine is more potent against aging when combined with Lipoic acid. According to these studies, lipoic acid restores cellular signaling and rejuvenates cells.

L-Carnitine Supplements
L-Carnitine Supplements

L-carnitine Side Effects

Although L-carnitine supplements are generally safe, there are a few mild symptoms one may experience. These include:

  • Nausea
  • Unpleasant body odor
  • Stomach cramps
  • Vomiting
  • Diarrhea
  • Heartburn

If the symptoms persist, please seek medical attention.

Usage and Dosing Consideration

The FDA does not have a daily recommended dose for L-carnitine supplementation because different therapies require different doses.

It, however, recommends taking 16.7mg/kilogram of body weight per day. That amounts to between 0.5g and 1g of L-carnitine per day for most people (23).

Most L-carnitine supplements have a daily dose of 2g daily. It would be best to consult your doctor on the appropriate dose for your specific use.

You might not even need to take L-carnitine supplements.

Risks and Precautions

As previously stated, there are some side effects associated with L-carnitine. If they persist, please seek medical attention.

If you are allergic to meat, you should also consult your doctor before taking L-carnitine supplements.

L-carnitine also falls within the FDA’s category B.

Drugs within category B have shown no adverse effects to the fetus when tested on animals. However, they have not been tested on a significant population of pregnant women to be considered completely safe for them.

If you are pregnant or lactating, you may want to stay away from this supplement or consult your doctor first. Parents should also consult a doctor before giving their children L-carnitine or any other supplements.

Adhere to the supplement dose directive to avoid adverse effects.


Is L-carnitine bad for your heart?

Most studies suggest that it lowers the risk of one getting cardiovascular diseases. Consult your doctor if you have any qualms about l-carnitine supplements before taking them.

Does L-carnitine help you lose weight?

While research into L-carnitine’s weight loss properties in animals shows modest results, human clinical trials are mostly inconclusive. Also, people react differently to different substances, so it just might work for you.

Should you take L-carnitine on an empty stomach?

Research studies recommend taking L-carnitine on an empty stomach to improve absorption rates (24).

Can L-carnitine make you poop?

A few studies highly recommend L-carnitine use in treating constipation.

The Bottom Line

L-carnitine presents quite the conundrum. While it has potential as a therapeutic agent, it is limited by insufficient research and contradictory findings.

Only a few of its purported benefits have been proven to be true. The lack of a standardized daily dose is the other problematic matter.

However, the good thing is that L-carnitine is generally safe. Remember, L-carnitine is also conditionally essential, so you may not need to take it.

But, if you decide to take L-carnitine supplements for any health reason, please consult your doctor first. If they approve, ensure you stick to the prescribed dose.