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Wellness

When to take L-carnitine

You can take this amino acid morning, noon, or night—depending on your goals
Leandra Beabout
By | Jul. 12, 2024 Medically reviewed by Gerardo Sison, Pharm.D.
A bottle of pills and free weights | When to take L-carnitine

Key takeaways

  • The best time to take L-carnitine supplements depends on the type of L-carnitine and the desired health benefit.

  • L-carnitine is absorbed most quickly when taken on an empty stomach or with a simple carbohydrate.

  • For optimum results, L-carnitine L-tartrate, which is often taken for athletic performance or fat loss, should be taken with a fast-acting carbohydrate 30 to 60 minutes before exercising.

In this article:

L-carnitine is a common form of carnitine, an amino acid found in animal products, especially red meat. A vegan diet may be low in carnitine content. According to the National Institutes of Health (NIH), it is also naturally produced in the human liver, kidneys, and brain. It is found in the highest concentrations in the brain and skeletal muscle. L-carnitine is vital for mitochondria function and fatty acid oxidation—essentially, it helps with energy production by transforming fat into fuel for the body’s cells.

If you’re considering an L-carnitine supplement, you might wonder: When is the best time to take it to get the most benefits? The answer depends on the form you’re taking and why you’re taking it—for exercise performance, post-workout muscle recovery, or brain function, for example.

What is L-carnitine?

L-carnitine is a nutrient that helps your body transform fat into energy. Your body produces it, and it is available as a supplement. Studies have shown that combining it with creatine and leucine may help increase muscle mass and improve physical performance.

Types of L-carnitine

L-carnitine is the most widely used form—and the form produced by your body—but there are four other types of carnitine you may come across.

  • L-carnitine L-tartrate: This form is known for its potent antioxidant properties, which support muscle recovery and minimize muscle damage. Recent studies have shown that L-carnitine L-tartrate can significantly improve short-term recovery among athletes. A randomized double-blind, placebo-controlled trial with eighty participants aged 21 to 65 found that daily supplementation for five weeks improved perceived recovery and reduced soreness. 
  • Acetyl-L-carnitine (ALCAR): Acetyl-L-carnitine has all of the benefits of regular L-carnitine, such as improved metabolism, but it more easily crosses the blood-brain barrier. This form has several effects on the brain and may be helpful for cognitive function, especially in cases of neurodegenerative diseases like dementia and mental health conditions like depression.
  • Propionyl-L-carnitine: This form of L-carnitine is best for vascular and circulatory health because it promotes nitric oxide production in the body. Research suggests that propionyl-L-carnitine may improve blood flow in people with lower extremity peripheral artery disease (PAD), which may help improve exercise performance.
  • D-carnitine: You should not take this form as a supplement. Animal studies have shown that it may cause fat to accumulate where it shouldn’t, causing liver problems or oxidative stress.

Ultimately, it’s best to consult a dietitian or healthcare provider when deciding which form is best for you.

When is the best time to take L-carnitine?

There is no standard recommended time of day to take L-carnitine supplements. The best timing depends on the form of L-carnitine and the benefits you seek. Timing is most important for people taking L-carnitine to improve exercise performance or recovery.

There are several potential health benefits of L-carnitine, including:

  • Athletic performance enhancement
  • Brain function support for those with Alzheimer’s disease and dementia
  • Diabetes control or prevention 
  • Cardiovascular protection
  • Weight loss

Morning

L-carnitine L-tartrate, the form most effective for athletic performance enhancement, is best taken on an empty stomach in the morning or before working out, says Patrick Nuzzo, DN, a doctor of naprapathy and the founder of the Southwest University of Naprapathic Medicine in Santa Fe, New Mexico.

Midday

Or, you can take it in the morning and before a workout. “Several studies recommend splitting supplemental L-carnitine intake into two or three doses,” says Rickelle Tallent, RDN, LD, owner of Tallent Nutrition & Wellness in Las Vegas, Nevada. “If the goal of taking supplemental L-carnitine is enhanced athletic performance and recovery, consider taking it 30 to 60 minutes before exercise along with fast-acting carbohydrates.”

Different types of L-carnitine may offer different benefits, with acetyl-L-carnitine often taken for its mental health benefits and improved effects on body fat metabolism. “Acetyl-L-carnitine is best taken in between meals and even better with coffee or green tea for added fat-burning properties,” says Christiane Matey, RDN, a North Carolina-based dietitian and founder of MINT Nutrition.

Nighttime

At least one case study has shown that L-carnitine may help with nighttime leg cramps, although this case study involved an individual who had experienced a stroke. People taking L-carnitine for post-workout recovery and reduced muscle soreness might find it beneficial to take their supplement at night, especially after days of high-intensity exercise.

Bottom line: There is no one-size-fits-all approach to timing L-carnitine supplementation. It is best absorbed on an empty stomach. However, its quick effectiveness means anyone taking it for athletic enhancement may experience greater benefits by taking it along with energy-boosting food shortly before a workout.

How much L-carnitine should I take daily?

“Optimal dosage is still undecided,” says Matey. There is no recommended dietary allowance (RDA) of L-carnitine. According to the NIH, common doses range from 3 milligrams (mg) to 5,000 mg daily, with an average 14% to 18% uptake rate. In other words, your body doesn’t actually absorb all of the L-carnitine in the supplement.

Experts agree that supplementation is considered generally safe, even long-term. However, Tallent says L-carnitine is not recommended for children, pregnant women, and people with seizure disorders.

Ultimately, anyone considering an L-carnitine supplement should consult a healthcare provider to determine the appropriate type and dosage.

What should not be taken with L-carnitine?

According to the NIH, several drugs have the potential to interact with L-carnitine. Certain medications can deplete natural L-carnitine levels and potentially cause carnitine deficiency:

If you’re taking one of these prescriptions, ask your healthcare provider if L-carnitine supplementation might be right for you. 

Before starting any new dietary supplements, it’s a good idea to talk to your healthcare provider or pharmacist about the risks and possible interactions with any drugs or vitamins.

Side effects of L-carnitine

L-carnitine supplements are considered generally safe, but taking high doses of L-carnitine (in excess of 3,000 mg) can increase your risk of side effects. Potential side effects of L-carnitine supplementation include:

  • Nausea
  • Vomiting
  • Stomach cramps
  • Diarrhea
  • A fishy body odor
  • Muscle weakness in people with chronic kidney disease
  • An increased risk of seizures in people with a seizure disorder

Additionally, Tallent says L-carnitine supplementation may also elevate trimethylamine-N-oxide (TMAO) blood levels—a risk factor for atherosclerosis, the medical term for clogged arteries.

Any unpleasant side effects should be reported to a healthcare provider who can advise whether it’s a good idea to stop taking L-carnitine and, if so, whether it would be helpful to taper off the supplement slowly. Dr. Nuzzo says abruptly stopping L-carnitine supplementation may cause temporary withdrawal effects such as fatigue, muscle cramping, irritability, or gastrointestinal symptoms.

Signs that L-carnitine supplements are working

It can take anywhere from three weeks to three months to start noticing the benefits of L-carnitine supplementation, according to Tallent. Dr. Nuzzo adds that increased energy and faster muscle recovery often kick in within the first month of supplementation.

Tallent says other signs that L-carnitine supplements are working may include:

  • Modest weight loss
  • Improved blood cholesterol levels
  • Improved blood pressure
  • Improved circulation
  • Improved blood sugar levels

If you have been taking L-carnitine supplements and don’t notice any improvements after three months, consider taking it with a carbohydrate source, such as fruit or fruit juice. Insulin released after eating a carbohydrate may improve the uptake of L-carnitine into muscle cells.

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