L carnitine side effects: the most important questions and answers

L Carnitin Nebenwirkungen: Die wichtigsten Fragen und Antworten

L-carnitine is particularly popular for weight loss or by top athletes, as the nutrient and the associated dietary supplement play an important role in energy production.

But what exactly is this nutrient L-carnitine and what does it do in our body. In this article we explain everything you need to know about L-carnitine. We also pay special attention to the side effects that can occur with L-carnitine and what you have to watch out for when taking it.

the essentials in brief

  • L-carnitine is an amino acid that is produced in the body. It helps the body produce energy and is important for heart and brain function, muscle movement and many other bodily processes. L-Carnitine is taken by mouth to increase L-Carnitine levels in people whose natural L-Carnitine levels are too low.
  • When taken by mouth, L-Carnitine is really safe when taken for up to 12 months. It can cause side effects such as nausea, vomiting, upset stomach, heartburn, diarrhea, and seizures
  • Possible alternatives to L-carntine are gabapentin and duloxetine, both of which have their pros and cons when used as alternatives.

Definition: What is L Carnitine?

L-Carnitine is a nutrient and dietary supplement. (1) It plays a crucial role in energy production by transporting fatty acids into the of your cells. The act as engines within your cells, burning these fats to create usable energy.

Your body can make L-carnitine from the amino acids lysine and methionine. In order for your body to be able to produce it in sufficient quantities, you also need a lot of vitamin C.

Meat in the pan

Red meat naturally contains a lot of L-carnitine (Image source: Egor Myznik / unsplash)

In addition to the L-carnitine produced in your body, you can also get small amounts from eating animal products like meat or fish. Vegans or people with certain genetic problems (2) may not be able to produce or get enough. This makes L-carnitine a conditionally essential nutrient.

What types of carnitine are there?

L-carnitine is the standard biologically active form of carnitine found in your body, in foods, and in most supplements. Here are some other types of carnitine:

  • D-Carnitine : This inactive form can cause carnitine deficiency in your body by inhibiting the absorption of other, more beneficial forms. (3)
  • Acetyl-L-Carnitine : Often referred to as ALCAR, it is possibly the most effective form for your brain. Studies suggest it could benefit people with neurodegenerative diseases. (4.5)
  • Propionyl-L-Carnitine : This form is good for circulatory problems such as peripheral vascular disease and high blood pressure. It can increase the production of nitric oxide, which improves blood flow. (6)
  • L-Carnitine L-Tartrate : Often added to sports nutrition supplements due to its rapid absorption rate. It can support muscle soreness and recovery from exercise. (7)

For most people, acetyl L-carnitine and L-carnitine seem to be the most effective for general use. However, you should always choose the form that best suits your personal needs and goals.

How does carnitine affect your body?

In cells, it helps transport fatty acids into the where they can be burned for energy.

L-Carnitine's primary role in your body involves l function and energy production.

About 98% of your L-carnitine stores are in your muscles, along with trace amounts in the liver and blood. L-Carnitine may help increase l function, which plays a key role in disease and healthy aging

Recent research illustrates the potential benefits of the different forms of carnitine, which can be used in various conditions, including heart and brain diseases

Background: What you should know about L-carnitine side effects

We have answered and summarized here which side effects could occur when taking L-carnitine and what you should do if this is the case.

What side effects can L-carnitine cause?

Most people tolerate L-carnitine well. However, some people may experience digestive side effects when taking L-carnitine. This includes:

  • stomach cramps
  • nausea
  • Vomit
  • Diarrhea

Some people also complain of a "fishy" body odor, which while not generally harmful, can be bothersome.

Some studies suggest that high levels of L-creatine may increase the long-term risk of cardiovascular disease, such as atherosclerosis.

What interactions can occur between L-carnitine and other medications?

If you are being treated with any of the following medications, you should not use carnitine without first talking to your doctor.

AZT : In a laboratory study, L-carnitine supplements protected muscle tissue from the toxic side effects of AZT, a drug used to treat HIV and AIDS. More studies are needed to find out if L-carnitine has the same effects in humans.

Doxorubicin : L-carnitine treatment may protect heart cells from the toxic side effects of doxorubicin, a cancer chemotherapy drug, without affecting the drug's effectiveness.

Isotretinoin (Accutan) : Accutane, a powerful drug used for severe acne, can cause liver problems, high cholesterol, and muscle pain and weakness as measured by a blood test. These symptoms are similar to those seen with carnitine deficiency. Researchers in Greece showed that a large group of people who experienced side effects from Accutane got better when taking L-carnitine compared to those taking a placebo.

Thyroid hormone : Carnitine can block thyroid hormone from entering cells and can theoretically make thyroid hormone replacement less effective.

Valproic acid (Depakote) : The antiepileptic drug valproic acid can lower blood levels of carnitine. Taking L-carnitine supplements can prevent deficiency and also reduce the side effects of valproic acid. However, taking carnitine may increase the risk of seizures in people with a history of seizures.

Blood-thinning medications : Carnitine may increase the risk of bleeding in people taking blood-thinning medications.

How dangerous is carnitine really?

However, it can cause side effects such as nausea, vomiting, upset stomach, heartburn, diarrhea, and seizures. It can also cause urine (8), breath, and sweat to have a "fishy" odor.

Avoid using D-Carnitine and DL-Carnitine. These forms of carnitine can block the effects of L-carnitine and cause symptoms similar to L-carnitine deficiency.

How high should L-carnitine be dosed?

The dosage for a wide range of applications can look like this, among other things:

problem dosage revenue
L-carnitine deficiency 990 mg 2 - 3 times a day
chest pain 900mg - 2g One to two divided doses daily for 2 weeks to 6 months
Heart failure and accumulation of fluid in the body 1.5-3g two divided doses daily up to 34 months
kidney disease 0.64 - 3g Daily for 3-52 weeks
hyperthyroidism 2-4g 2 - 4 months daily
male infertility 2-3g Up to three divided doses daily for 2-24 weeks
swelling of the heart 100 mg daily for 4 days
Hormonal disorders causing enlargement of the ovaries 250 mg Daily for 2 weeks
toxic side effects from valproic acid 50-100mg three or four divided doses daily

Note, however, that L-Carnitine can have different effects from person to person. So if side effects should occur, discontinue L-carnitine and consult your doctor.

When should I not take L-carnitine?

L-carnitine is not recommended in the following cases:

pregnancy and breastfeeding

There is not enough reliable information to know if L-carnitine is safe to use during pregnancy.

L-carnitine may be safe for breastfeeding women when taken by mouth in amounts recommended by a health care provider.

Small amounts of L-carnitine have been given to infants in breast and formula milk with no reported side effects. The effects of large amounts ingested by a nursing mother are unknown. (9)

Pregnant woman

Stay safe and avoid using L-carnitine while pregnant (Image source: Anastasiia Chepinska/unsplash)

With children

L-carnitine is possibly safe when taken appropriately orally or intravenously (intravenously) for short periods. It has been used safely in the mouth for up to 6 months. (10,11,12)

kidney failure

The use of DL-carnitine when administered intravenously (intravenously, intravenously) after dialysis has been reported to cause symptoms such as muscle weakness and eye drooping. L-carnitine does not appear to have this effect. (13)

Underactive thyroid (hypothyroidism)

Taking L-carnitine can worsen symptoms of an underactive thyroid.


L-carnitine supplementation appears to make seizures more likely in people who have had seizures before. If you've had an attack, don't use L-carnitine.

Is L-Carnitine Worth the Risk?

Your L-carnitine levels are affected by how much you eat and how much your body produces.

For this reason, L-carnitine levels are often lower in vegetarians and vegans as they limit or avoid animal products. (14)

As such, vegetarians and vegans may want to consider L-carnitine supplements. (15) However, there are no studies that have confirmed the benefits of carnitine supplements in these specific populations.

Older adults may also benefit from L-Carnitine supplements. Research shows that your levels tend to decrease as you age. (16.17)

In one study, 2 grams of L-carnitine reduced fatigue and increased muscle function in older adults. Other research shows that acetyl-L-carnitine may also help improve brain health and function as we age. (18.19)

In addition, the risk of deficiency is higher for people with diseases such as cirrhosis and kidney disease. If you suffer from any of these conditions, supplementation may be beneficial. (20)

As with any supplement, consult your doctor before taking L-Carnitine.

What alternatives are there to L-carnitine?

Two common alternatives to L-carnitine are gabapentin and duloxetine.


Gabapentin is an antiepileptic, also called an anticonvulsant. It affects chemicals and nerves in the body that are involved in causing seizures and some types of pain.

Gabapentin is used with other medicines to treat partial seizures in adults and children at least 3 years of age. Gabapentin is also used to treat neuropathic pain (nerve pain) caused by herpes viruses or shingles (herpes zoster) in adults.

Gabapentin can cause life-threatening breathing problems, especially in older adults or people with COPD. Get emergency medical attention if you have trouble breathing.

Some people have thoughts about suicide or behavior changes while taking gabapentin. Stay alert if your mood or symptoms change. Report any new or worsening symptoms to your doctor. Avoid driving or engaging in dangerous activities until you know how gabapentin affects you. Dizziness or light-headedness can lead to falls, accidents or serious injuries.

Don't suddenly stop taking gabapentin even if you feel fine.


Duloxetine is a selective serotonin and norepinephrine reuptake inhibitor antidepressant (SSNRI). Duloxetine affects chemicals in the brain that can become unbalanced in people with depression. It is also used to treat major depressive disorder in adults. It is also used to treat generalized anxiety disorder in adults and children who are at least 7 years old.

Duloxetine is also used in adults to treat nerve pain caused by diabetes (diabetic neuropathy) or chronic muscle or joint pain (such as low back pain and osteoarthritis pain).

Duloxetine is also used to treat fibromyalgia (a chronic pain disorder) in adults and children aged 13 and over.

Do not take duloxetine within 5 days before or within 14 days of taking an MAOI such as isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, or tranylcypromine. A dangerous drug interaction could occur.

Some young people have suicidal thoughts when first taking an antidepressant. Stay alert if your mood or symptoms change. Report any new or worsening symptoms to your doctor.

Do not stop taking duloxetine without first talking to your doctor.

Both alternatives therefore have their advantages and disadvantages. It is therefore important to weigh these carefully beforehand and then make a decision with a doctor.


L-carnitine is an amino acid that the body produces naturally. In healthy people, the liver and kidneys produce and store enough of the compound to prevent deficiency.

People with L-carnitine deficiency may need to take the active ingredient through food or as a dietary supplement. It is advisable to speak to a doctor before taking an L-carnitine supplement.

Some people may wish to take L-carnitine supplements for their potential benefits, such as supporting athletic performance or weight loss.

However, there can be a number of side effects that can vary from person to person. If side effects of any kind occur, it is advisable to reduce the dosage or discontinue L-carnitine altogether.


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