Acetyl-L-Carnitine (ALCAR): Benefits, Side Effects and ALCAR vs L-Carnitine

Acetyl-L-carnitine, often shortened to ALCAR, is L-carnitine with an acetyl group attached, and it is the main carnitine ester your body makes and uses. The most common acetyl-L-carnitine side effects are digestive: at about 3 g a day, carnitine supplements can cause nausea, vomiting, stomach cramps, diarrhea and a fishy body odor. Check with a clinician first if you take a blood thinner, thyroid medicine or seizure medicine.

Carnitine helps move fats into your mitochondria so they can be burned for energy, and the acetyl group gives ALCAR a second role as a building block the body can use for energy and for acetylcholine, a messenger in the brain. This guide explains what ALCAR does, what the research shows, how it compares with L-carnitine and L-carnitine tartrate, how much people take, and the side effects to know about.

It is educational, not medical advice.

Key Takeaways

• What it is: ALCAR is L-carnitine with an acetyl group. Your body makes carnitine from the amino acids lysine and methionine and also gets it from food, mainly red meat.
• What it does: carnitine carries long-chain fatty acids into the mitochondria to be used for energy; the acetyl group can be used for energy or to make acetylcholine.
• ALCAR vs L-carnitine: they share the same carnitine pool in the body. ALCAR is the form usually studied for the brain and nerves, while L-carnitine L-tartrate is the form usually studied for exercise recovery.
• Research: in a trial of 96 adults aged 71 to 88 with ongoing tiredness, ALCAR lowered physical and mental fatigue scores. In old rats it partly restored markers of mitochondrial function.
• Side effects: around 3 g a day of carnitine can cause nausea, stomach cramps, diarrhea and a fishy body odor. Check with a clinician if you take a blood thinner or thyroid medicine.

What Is Acetyl-L-Carnitine (ALCAR)?

Carnitine is a compound that helps transport long-chain fatty acids into the mitochondria, the parts of your cells that turn fuel into energy. Your body makes it in the liver, kidneys and brain from the amino acids lysine and methionine. Food adds more: red meat is the richest source, poultry, fish and dairy provide some, and plant foods provide very little. A typical diet that includes meat provides about 24 to 145 mg of carnitine a day, compared with about 1.2 mg on a vegan diet (NIH Office of Dietary Supplements, 2023).

In the body, carnitine exists as plain L-carnitine and as a family of esters. Acetyl-L-carnitine is the most important of these esters, both in amount and in function (Rebouche, 2004). Its acetyl group can be burned for energy, used to make the brain messenger acetylcholine, or built into other molecules (Ferreira, 2017).

Carnitine is not a vitamin. Your body makes its own supply, which is why people who eat little meat still have carnitine. ALCAR is sold as a supplement, often labeled acetyl-L-carnitine HCl, which is ALCAR in a hydrochloride salt form.

What Does Acetyl-L-Carnitine Do?

ALCAR has two jobs, one from each part of the molecule:

• The carnitine part helps move fatty acids into mitochondria so they can be used for energy (Traina, 2016).
• The acetyl part acts as an acetyl donor. It can feed energy production, serve as a building block for acetylcholine, or be used to make other brain chemicals and lipids (Ferreira, 2017).

Because of that acetyl group, much of the ALCAR research focuses on the brain and nervous system, while L-carnitine research focuses more on muscle and exercise. For more on how cells make energy, see our guide to cellular energy and mitochondrial health.

Acetyl-L-Carnitine Benefits: What Studies Show

Fatigue in older adults

In a trial of 96 adults aged 71 to 88 who reported ongoing tiredness, the group given ALCAR had lower physical and mental fatigue scores at the end of treatment than the comparison group. Their daily function and scores on a standard test of memory and thinking also improved more (Malaguarnera, 2008).

Mitochondria and aging

In a well-known animal study, old rats given ALCAR in their drinking water for a month regained several markers of mitochondrial function that decline with age, including oxygen use, and they moved around more. The same study also found higher oxidant production per unit of oxygen used and lower glutathione in the treated old rats, so the authors noted ALCAR might increase oxidative stress (Hagen, 1998). A later review by the same group described ALCAR improving fat burning in the mitochondria of old rats, noted that it did not appear to improve antioxidant status in the aging heart, and suggested pairing it with the antioxidant alpha-lipoic acid (Hagen, 2002). These are animal results.

Brain and acetylcholine

Reviews describe ALCAR as affecting brain energy metabolism, cell membranes and the way nerve cells signal to each other, and as supplying acetyl groups for acetylcholine (Pettegrew, 2000; Ferreira, 2017). If you are interested in acetylcholine, our guides to citicoline benefits and citicoline vs alpha GPC cover choline, the other half of that molecule. How much choline citicoline carries is set out on our citicoline (CDP-choline) reference page.

Acetyl-L-Carnitine vs L-Carnitine

ALCAR and L-carnitine belong to the same carnitine pool in the body, and ALCAR is the most important of the carnitine esters in it (Rebouche, 2004). Some ALCAR is broken down to L-carnitine in the gut wall during absorption, but taking 2 g of ALCAR a day raised blood ALCAR levels by 43 percent, so at least part of it is absorbed intact (Rebouche, 2004).

Supplements are absorbed less well than carnitine from food. The body absorbs about 63 to 75 percent of the carnitine in meals but only about 14 to 18 percent of an L-carnitine supplement (NIH Office of Dietary Supplements, 2023).

Form	What it is	Usually studied for
Acetyl-L-carnitine (ALCAR)	L-carnitine with an acetyl group	Brain, nerves and fatigue in older adults
L-carnitine	The plain form, also found in food	Muscle carnitine, older adults, general use
L-carnitine L-tartrate (LCLT)	L-carnitine bound to tartaric acid	Recovery after hard exercise

ALCAR vs L-carnitine L-tartrate

L-carnitine L-tartrate is the form usually used in exercise studies. In a crossover trial, 10 resistance-trained men took L-carnitine L-tartrate providing 2 g of L-carnitine a day for 3 weeks. After a hard squat workout, markers of muscle damage were lower, and the area of muscle disruption seen on MRI was 41 to 45 percent of that with placebo (Volek, 2002). A 2018 review of L-carnitine and recovery reached similar conclusions and noted studies in older adults showing more muscle mass and less physical and mental fatigue (Fielding, 2018).

In short, L-carnitine L-tartrate is the form studied for workouts and recovery, while ALCAR is the form studied for the brain, nerves and fatigue in older adults.

Acetyl-L-Carnitine Dosage and When to Take It

Carnitine has no official upper limit (NIH Office of Dietary Supplements, 2023). Supplement studies have used 0.5 to 6 g of L-carnitine (Rebouche, 2004), and studies in healthy adults lasting 12 to 24 weeks used 1 to 4 g a day (Sawicka, 2020). The ALCAR absorption data above came from 2 g a day.

• Follow your label. Start at the low end and stay at the label dose.
• Same time each day. A routine makes daily use easier, so pick a time that fits your day.
• With food if your stomach is sensitive. Stomach upset is the most common complaint.
• Watch the total. Side effects are more likely at about 3 g a day.

Our OEA Supplement includes 200 mg of acetyl-L-carnitine per 2-capsule serving, as one part of a formula built around OEA, so it is well below the amounts used in the studies above. For how OEA itself works, see our OEA guide and the OEA ingredient page.

Acetyl-L-Carnitine Side Effects at a Glance

Acetyl-L-carnitine side effects are tied to the amount taken. The digestive effects listed for carnitine are linked to about 3 g a day, and daily use is how it has been studied: 1 to 4 g a day for 12 to 24 weeks in healthy adults. For comparison, our OEA Supplement contains 200 mg of acetyl-L-carnitine per 2-capsule serving.

Group	What to know
Common, at about 3 g a day	Nausea, vomiting, stomach cramps, diarrhea and a fishy body odor. Stomach upset is the most common complaint.
Lab marker	Fasting TMAO rose in L-carnitine studies lasting 12 to 24 weeks, without changes in the inflammation or oxidative stress markers measured.
Less common	Seizures in people who have a seizure disorder, and muscle weakness in people with uremia from kidney failure.
Who should check first	Anyone taking a blood thinner, thyroid medicine or seizure medicines such as valproic acid; anyone with low thyroid function, a seizure disorder or kidney disease; and anyone pregnant or breastfeeding.

Starting at the low end of your label, taking it with food and adding up carnitine from every product you use all help. Our OEA Supplement also contains PEA and green tea extract, covered in palmitoylethanolamide (PEA) and green tea extract and EGCG.

Acetyl-L-Carnitine Side Effects

At doses of about 3 g a day, carnitine supplements can cause nausea, vomiting, stomach cramps, diarrhea and a fishy body odor. Gut bacteria also turn unabsorbed carnitine into a compound called TMAO, which might increase the risk of heart disease (NIH Office of Dietary Supplements, 2023). A systematic review of healthy adults taking L-carnitine for 12 to 24 weeks found that fasting TMAO rose, without changes in the inflammation or oxidative stress markers measured, and called for longer studies (Sawicka, 2020).

Less common side effects and how dose matters

Beyond stomach upset and body odor, the NIH Office of Dietary Supplements lists two less common carnitine side effects: seizures in people who have a seizure disorder, and muscle weakness in people with uremia, the buildup of waste in the blood that comes with kidney failure (NIH Office of Dietary Supplements, 2023). If you have a seizure disorder or kidney disease, talk with your clinician before taking any carnitine product.

ALCAR side effects are tied to the amount taken. The digestive effects and body odor are linked to doses of about 3 g a day, and trials of acetyl-L-carnitine in older adults with cognitive decline or dementia used 1.5 to 3 g a day for 3 to 12 months (NIH Office of Dietary Supplements, 2023). Starting at the low end of your label, taking it with food and keeping your total from all products in view all help. Stop and seek advice if anything unusual appears.

Medicines and who should check first

• Blood thinners. Case reports linked L-carnitine with a stronger effect of the blood thinner acenocoumarol (Martinez, 1993; Bachmann, 2004). If you take any blood thinner, check with your clinician first.
• Thyroid. L-carnitine blocks thyroid hormone from entering cell nuclei, and it has been studied in people with an overactive thyroid for that reason (Benvenga, 2004). If you have low thyroid function or take thyroid medicine, ask your clinician before using carnitine.
• Seizure medicines. Valproic acid and some other anticonvulsants lower carnitine levels (NIH Office of Dietary Supplements, 2023), so anyone taking them should let their doctor manage carnitine.
• Pregnancy, breastfeeding, kidney disease or any ongoing health condition: talk with a clinician before taking ALCAR.

For other ingredients often used for daily energy, see supplements for energy without the crash, PQQ benefits and creatine for brain health, and our metabolic health and energy balance guide. Reference facts on PQQ, including the daily amounts used in human trials, are on our PQQ ingredient page.

Frequently Asked Questions

What is ALCAR?

ALCAR is short for acetyl-L-carnitine, L-carnitine with an acetyl group attached. It is the most important carnitine ester in the body and is sold as a supplement, often as acetyl-L-carnitine HCl.

Is acetyl-L-carnitine the same as L-carnitine?

No, but they are closely related and part of the same carnitine pool in the body. ALCAR carries an extra acetyl group that can be used for energy or to make acetylcholine.

Which is better, acetyl-L-carnitine or L-carnitine tartrate?

It depends on your goal. L-carnitine L-tartrate is the form used in exercise recovery studies, while ALCAR is the form usually studied for the brain, nerves and fatigue in older adults.

How much acetyl-L-carnitine should I take?

Follow your label. Carnitine studies in healthy adults used 1 to 4 g a day, and side effects become more likely at about 3 g a day.

When is the best time to take acetyl-L-carnitine?

Take it at the same time each day, as your label directs, and with food if your stomach is sensitive.

What are the side effects of acetyl-L-carnitine?

At about 3 g a day, carnitine can cause nausea, vomiting, stomach cramps, diarrhea and a fishy body odor. It can also raise TMAO levels. Check with a clinician if you take a blood thinner, thyroid medicine or seizure medicine.

Is ALCAR a vitamin?

No. Your body makes carnitine from the amino acids lysine and methionine, and you also get it from food, mainly red meat.

Can you take acetyl-L-carnitine with alpha-lipoic acid?

They are often combined, and the pair has been studied together in aging rats. If you take a combination, follow the label and check with a clinician if you take other medicines.

What does acetyl-L-carnitine do for the body?

It does two jobs. The carnitine part helps carry long-chain fatty acids into your mitochondria so they can be used for energy. The acetyl part can be burned for energy, used to make acetylcholine, a messenger in the brain, or built into other brain chemicals and lipids. That is why ALCAR research centers on the brain, nerves and fatigue in older adults.

What is acetyl-L-carnitine HCl?

Acetyl-L-carnitine HCl is ALCAR in a hydrochloride salt form. Its benefits and side effects are those of ALCAR itself, covered above. When you compare labels, check the amount of acetyl-L-carnitine per serving, and add up any carnitine you get from other products so your total stays well below about 3 g a day.

Is it safe to take acetyl-L-carnitine every day?

Daily use is how it has been studied. Carnitine has no official upper limit, studies in healthy adults used 1 to 4 g a day for 12 to 24 weeks, and acetyl-L-carnitine trials in older adults ran for 3 to 12 months. Side effects become more likely at about 3 g a day, and fasting TMAO rose in L-carnitine studies lasting 12 to 24 weeks, so follow your label and check with a clinician if you take medicines.

Does ALCAR cause a fishy body odor?

It can. A fishy body odor is one of the side effects listed for carnitine supplements at about 3 g a day, along with nausea, vomiting, stomach cramps and diarrhea. It is linked to the amount taken, so staying at your label dose matters. Our OEA Supplement contains 200 mg of acetyl-L-carnitine per 2-capsule serving, well below that level.

Does acetyl-L-carnitine upset your stomach?

It can at higher amounts. Stomach upset is the most common complaint, and nausea, cramps and diarrhea are linked to about 3 g a day. Taking it with food and starting at the low end of your label help.

Who should check with a clinician before taking acetyl-L-carnitine?

Anyone who takes a blood thinner, thyroid medicine or seizure medicine, has low thyroid function, a seizure disorder or kidney disease, or is pregnant or breastfeeding.

Does acetyl-L-carnitine interact with medications?

It can. Case reports linked L-carnitine with a stronger effect of the blood thinner acenocoumarol, L-carnitine blocks thyroid hormone from entering cell nuclei, and valproic acid and some other anticonvulsants lower carnitine levels.

Sources

• NIH Office of Dietary Supplements. Carnitine: Fact Sheet for Health Professionals. Updated April 17, 2023. ods.od.nih.gov
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These statements have not been evaluated by the Food and Drug Administration. This content is for education and is not medical advice. Our products are not intended to diagnose, treat, cure or prevent any disease. Talk with a healthcare provider before starting a new supplement if you are pregnant, breastfeeding or taking medication.