L-carnitine, also known as levocarnitine, is an amino acid that your liver, kidneys, and brain generate from two other amino acids—lysine and methionine. You can also get carnitine from foods and supplements. Its main roles in the body are helping to convert fats into energy and removing toxic compounds from cells.
Popular claims say L-carnitine supplements help with weight loss and athletic performance, but research doesn’t fully support these claims. However, research has found some promise in L-carnitine's ability to help with brain, reproductive, and cardiovascular health.
Research has found that L-carnitine may support various aspects of brain health. For example, studies have found it may help slow cognitive decline associated with dementia and Alzheimer’s disease.
Alzheimer’s disease can be treated by increasing acetylcholine levels. Evidence suggests carnitine may be conditionally essential for people with Alzheimer’s since it might support acetylcholine synthesis and removal of toxins from cells.
A research review found some promising results regarding the effects of L-carnitine supplementation on dementia, but the results were still mixed and warrant further research.
Some studies have also found that L-carnitine was more effective than a placebo for treating depression. Other research found that L-carnitine was as effective as two depression medications—Prozac (fluoxetine) and Deniban (amisulpride)—in participants with persistent depressive disorder. However, more studies with bigger sample sizes are needed to further evaluate these mood-related benefits.
May Prevent Cardiovascular Disease
Carnitine plays an important role in supporting cardiovascular health. However, research is still evaluating the effects of L-carnitine supplementation on cardiovascular health.
A meta-analysis that included over 3,500 adults who had heart attacks evaluated the effects of five days to 12 months of L-carnitine supplementation compared to a placebo. The researchers found that L-carnitine significantly reduced the rate of mortality, ventricular arrhythmias, and new-onset angina, regardless of the dose or duration of L-carnitine supplementation.
However, some studies have found that L-carnitine supplementation may worsen heart health. It’s metabolized by the microorganisms in your intestines to form trimethylamine-N-oxide (TMAO), which is associated with higher cardiovascular disease risk.
Since the results are mixed on the effects of L-carnitine supplementation on heart health, more research is needed to further explore this area.
Some studies have found promising benefits of L-carnitine supplementation on markers of type 2 diabetes. For example, a large meta-analysis found that L-carnitine supplementation significantly improved fasting blood glucose, hemoglobin A1C, and HOMA-IR—a marker of insulin resistance. This was particularly true for doses at or above 2 grams (g) per day for at least 12 weeks.
The study authors note this may be due to L-carnitine’s role in maintaining insulin sensitivity and metabolizing fat and glucose.
May Support Reproductive Health
L-carnitine supplementation may improve fertility, particularly for males and people with polycystic ovary syndrome (PCOS).PCOS is a hormonal condition that occurs when the ovaries make more androgens (the male sex hormone) than needed.
A meta-analysis of studies involving about 200 men struggling with infertility found that 1–3 g/day of L-carnitine supplementation for two to six months improved sperm motility and morphology (the size and shape of sperm).
Another review found that L-carnitine supplementation improved sperm motility and concentration. However, this didn’t translate to more pregnancies.
One study of 280 women with PCOS found that participants who took 3 g of L-carnitine in addition to metformin and the fertility drug clomiphene-citrate had higher ovulation and pregnancy rates than the women who took the two medications without L-carnitine. Notably, these were women who were clomiphene-resistant, so the fertility medication alone hadn’t worked for them before.
The best food sources of carnitine are animal products, but you can also find them in some vegan foods. Here are the best sources of carnitine:
- Beef steak: 42–122 milligrams (mg) per 3 ounces(oz)
- Ground beef: 65–74 mg per 3 oz
- Whole milk: 8 mg per cup
- Codfish: 3–5 mg per 3 oz
- Chicken breast: 2–4 mg per 3 oz
- Ice cream: 3 mg per 0.5 cups
- Cheddar cheese: 2 mg per 2 oz
- Whole-wheat bread: 0.2 mg per 2 slices
- Asparagus: 0.1 mg per 0.5 cups
How To Take L-Carnitine
Most L-carnitine supplements come in capsules, tablets, or powder form. You can take it any time of day, but most people recommend taking it on an empty stomach or with carbohydrates for optimal absorption.
Many supplement manufacturers recommend taking a capsule three times daily to spread out your intake. Most studies have found benefits after 12–24 weeks of L-carnitine supplementation in doses of 1–4 g/day.
Dosage
Your body needs about 15 mg per day of carnitine from a combination of its own production of carnitine, food, and supplements. Most people meet their carnitine needs from the body’s production alone. Even people following a vegetarian diet produce close to 15 mg/day and will likely obtain the rest from dietary sources of carnitine.
There is no specific dosage recommendation for L-carnitine supplements since our bodies produce it naturally. Many supplements provide doses of 1–2 g/day.
L-carnitine is generally a safe supplement, especially when taken in moderate doses below 2 g/day. Some cases have shown pregnant people deficient in carnitine safely continued taking L-carnitine throughout pregnancy with no serious adverse effects.
Still, larger studies are needed to confirm the safety of L-carnitine during pregnancy. If you are considering taking L-carnitine during pregnancy, do so under the guidance of a trusted healthcare provider.
While breastfeeding, L-carnitine supplementation may be warranted if you are deficient in carnitine. However, there isn’t data on the safety of carnitine supplementation in breastfeeding individuals without a carnitine deficiency.
People with seizure disorders or uremia (a condition in which kidneys don't function well enough to remove waste) should speak with a healthcare provider before taking L-carnitine, as it can cause muscle weakness and seizures when taken in excess.
Studies have not found benefits of L-carnitine supplementation on athletic performance. Researchers have raised concerns about the use of L-carnitine supplementation in this population, given the potentially harmful production of TMAO (associated with higher cardiovascular disease risk).
Potential Drug Interactions
Certain drugs may affect carnitine levels in the body, so it’s extra important to speak with a trusted healthcare provider before taking L-carnitine if you’re taking the following medications:
- Certain antibiotics: Pivalate-conjugated antibiotics used to prevent urinary tract infections can deplete carnitine levels if taken long-term. However, this doesn’t appear to lead to illness.
- Certain anticonvulsants: Anticonvulsants like valproic acid, phenobarbital, phenytoin, and carbamazepine reduce blood carnitine levels. Intravenous (IV) carnitine—injected into a vein—may help treat valproic acid toxicity that can lead to encephalopathy (brain dysfunction).
What To Look For
The U.S. Food and Drug Administration (FDA) does not verify the purity and potency of dietary supplements. If you want to purchase an L-carnitine supplement, look for a product that is third-party tested for ingredient purity and potency. Reputable third-party testers include USP, NSF, and ConsumerLab.com.
You can also ask a healthcare provider to recommend a reputable brand.
Can You Take Too Much L-Carnitine?
There is no tolerable upper limit established for L-carnitine. Some research shows supplement doses above 3 g/day can cause unpleasant side effects. For people with uremia or seizure disorders, excess carnitine can cause muscle weakness and seizures.
Side Effects of L-Carnitine
While L-carnitine is generally safe, taking too much L-carnitine can cause unpleasant side effects. These include:
- Abdominal cramps
- Nausea
- Vomiting
- Diarrhea
- Fishy body odor
L-carnitine is an amino acid that your liver, kidneys, and brain generate from two other amino acids—lysine and methionine. You can also get carnitine from supplements and foods like meat and dairy.
Supplementing with L-carnitine may help support brain and heart health, type 2 diabetes management, and fertility. While it's often touted for aiding weight loss and athletic performance, these benefits are not backed by research.
