L-arginine is an amino acid. Amino acids are the building blocks of proteins and divided into essential and nonessential categories. Nonessential amino acids are made in the body, but essential amino acids are not. As such, they must be provided through dietary intake (1).

L-arginine is considered semi-essential or conditionally essential, meaning that it becomes essential under certain circumstances and conditions, including pregnancy, infancy, critical illness, and trauma (2).

It’s necessary for the production of nitric oxide, a signaling molecule that’s needed for a variety of bodily processes and functions, including blood flow regulation, mitochondrial function, and cellular communication (1, 3).

Additionally, it acts as a precursor to other amino acids, including glutamate, proline, and creatine, and is essential for the health and functioning of your immune system.

Arginine is necessary for the development of T-cells, which are white blood cells that play central roles in immune response (2).

Because L-arginine has so many critical roles in your body, a deficiency in this amino acid can disrupt cellular and organ function and lead to serious adverse health outcomes (2).

L-arginine is produced in several ways. It can be synthesized from the amino acid citrulline through the breakdown of body proteins, or it can be obtained through dietary protein intake (2).

It’s concentrated in certain protein-rich foods, including meat, poultry, dairy, nuts, soy products, and fish. The average daily intake of L-arginine from foods is reported to be 4–6 grams (4).

For reference, research shows that a typical Western diet provides between 25–30% of total arginine present in the body (5).

Additionally, L-arginine can be obtained by taking supplements. L-arginine supplements are widely available and can be found in powder, liquid, capsule, and tablet form at grocery stores, supplement stores, and online.

This article mainly focuses on the benefits and uses of L-arginine supplements.

L-arginine supplements are taken by many populations, including athletes and those who have certain medical conditions like high blood pressure, for a variety of reasons. They’re also used in the clinical setting to treat critically ill people or those with wounds.

Research has shown that L-arginine may offer a variety of potential benefits when used as a supplement. However, results are mixed, and L-arginine may not be as effective for some conditions as many supplement companies claim.

Athletic performance enhancement

Limited evidence suggests that L-arginine supplements may enhance exercise performance by increasing nitric oxide in the body, which improves blood flow and oxygenation to muscles.

For example, a 2017 randomized study in 56 male soccer players found that treatment with 2 grams of L-arginine daily for 45 days significantly increased sport performance, compared with a placebo group (6).

Another small study in 9 men demonstrated that those who drank a beverage containing 6 grams of L-arginine 1 hour before intense exercise had significantly increased blood levels of nitric oxide and were able to exercise longer, compared with a placebo group (7).

However, most studies investigating this relationship have found that L-arginine is not beneficial for improving athletic performance (8, 9, 10, 11).

L-citrulline, a precursor to L-arginine that’s discussed later in this article, may be a better choice for boosting athletic performance.

Blood pressure regulation

L-arginine supplements may benefit those with high blood pressure.

Studies have shown that taking L-arginine supplements may help lower both your systolic (the top number) and diastolic (the bottom number) blood pressure readings.

L-arginine is needed for the production of nitric oxide, which is necessary for the relaxation of the cells that make up blood vessels, as well as blood pressure regulation.

A 2016 review of 7 studies found that supplementing with L-arginine by both oral and intravenous (IV) administration significantly reduced systolic and diastolic blood pressure in adults with high blood pressure by up to 5.4 mm/Hg and 3.1 mm/Hg, respectively (1).

Management of critical illness

Arginine becomes essential when your body is compromised due to conditions like infection and trauma, and your arginine needs significantly increase due to physiologic demands.

Under these circumstances, your body can no longer fulfill your arginine needs, which must be met through external sources.

Arginine depletion during critical illness or after surgery leads to serious adverse effects, including impaired immune function and blood flow. To avoid these potential complications, arginine supplements are used frequently in the clinical setting to treat a variety of conditions.

For example, oral or IV arginine is commonly used to treat serious infections like necrotizing enterocolitis in infants, cases of sepsis, burns, chronic disease, and wounds, as well as in pre- and post-surgical and trauma patients (5, 12).

Blood sugar regulation

Research shows that L-arginine may benefit those with diabetes by improving glucose metabolism and insulin sensitivity (13).

L-arginine is needed for the production of nitric oxide. Nitric oxide plays important roles in cellular function and how your body responds to insulin, a hormone that shuttles blood sugar from your blood into cells, where it’s used for energy.

Therefore, increasing nitric oxide availability may help enhance the function of cells that secrete insulin and help your body use blood sugar more efficiently.

Some research has shown that long-term treatment with L-arginine supplements may prevent diabetes in at-risk populations (14).

A study in 144 people with impaired blood sugar regulation found that treatment with 6.4 grams of L-arginine per day for 18 months reduced the chances of diabetes development over a 90-month period, compared with a placebo group (14).

Other potential benefits

In addition to the potential benefits listed above, some research suggests that L-arginine supplements may be helpful when used in the following ways:

  • Treatment of erectile dysfunction. A 2019 review of 10 studies found that taking arginine supplements in doses ranging from 1.5–5 grams daily significantly improved erectile dysfunction, compared with a placebo or no treatment (15).
  • Improving blood flow. Some evidence suggests L-arginine supplements may improve blood vessel function and blood flow in specific populations. However, study results are conflicting, and many have found that L-arginine has no benefit (16, 17, 18, 19).
  • Treating and preventing preeclampsia. Studies have demonstrated that treatment with L-arginine during pregnancy may help prevent and treat preeclampsia, a dangerous condition characterized by high blood pressure and protein in the urine (20, 21).

This list is not exhaustive, and L-arginine has been studied for its potential beneficial effects on various conditions, including obesity, heart disease, cancer, polycystic ovary syndrome (PCOS), infertility, and anxiety, either used on its own or in combination with other supplements.

However, research on the effects of L-arginine in people with these and many other conditions is limited and inconclusive, highlighting the need for future studies (22).

In addition to the potential benefits and uses above, many people take L-arginine supplements for a variety of other reasons, including reducing the risk of the common cold and boosting weight loss. Yet, many of these purported benefits aren’t backed by scientific research.

Overall, research has shown that L-arginine is safe and generally well tolerated when taken in supplement form, even when taken daily over long periods of 1 year or more (14).

However, it can cause unpleasant side effects, including bloating, abdominal pain, nausea, and diarrhea, especially when taken in large doses of 9 grams or more per day (1).

Yet, one 90-day study in 142 adults demonstrated that a daily dose of up to 30 grams was well tolerated and not associated with any adverse effects, suggesting that even very high doses of L-arginine are usually safe, at least in the short term (23).

Even though they have a strong safety profile, arginine supplements should be avoided by certain populations.

For example, those with asthma, cirrhosis of the liver, kidney disease, low blood pressure, and guanidinoacetate methyltransferase deficiency — an inherited disorder that affects arginine metabolism, should avoid L-arginine due to the potential for adverse effects (22).

Doses of L-arginine vary widely depending on what it’s being used to treat.

For example, studies investigating the effects of L-arginine on blood pressure have used doses of 6–30 grams per day for 2–24 weeks (22, 23).

In those with erectile dysfunction, research has suggested that supplementing daily with 1.5–5 grams of L-arginine may significantly improve symptoms (15, 22).

When used to treat preeclampsia, the dose typically ranges from 3–4 grams daily for up to 12 weeks, or until delivery under a doctor’s supervision. L-arginine may also be given intravenously to pregnant women with high blood pressure in the clinical setting (22, 24).

Although higher doses are often used in research and clinical settings, it’s recommended that daily dosing of L-arginine be kept under 9 grams per day to avoid potential gastrointestinal side effects, including nausea, diarrhea, and bloating.

Like other single amino acids, it’s recommended to take L-arginine between meals for maximum absorption (25).

As mentioned above, arginine is generally considered safe, even when used in high doses.

However, it’s possible to take too much arginine, which is especially dangerous for children. This is explained in greater detail later in this article.

L-arginine may interact with certain medications, including (22):

  • Blood-pressure-lowering medications: enalapril (Vasotec), losartan (Cozaar), amlodipine (Norvasc), furosemide (Lasix), etc.
  • Erectile dysfunction medications: sildenafil citrate (Viagra), tadalafil (Cialis), etc.
  • Blood-thinning medications: clopidogrel (Plavix), enoxaparin (Lovenox), heparin, warfarin (Coumadin), etc.
  • Antidiabetic medications: insulin, pioglitazone (Actos), glipizide (Glucotrol), etc.
  • Medications that increase blood flow: nitroglycerin (Nitro-Dur, Nitro-Bid, Nitrostat), isosorbide ( Sorbitrate, Imdur, Isordil), etc.
  • Diuretic medications: amiloride (Midamor), and triamterene (Dyrenium), spironolactone (Aldactone), etc.

Additionally, L-arginine may interact with certain supplements and substances, including (22):

  • Herbs and supplements with blood-pressure-lowering effects: coenzyme Q10, cat’s claw, fish oil, Lycium, stinging nettle, theanine, etc.
  • Herbs and supplements that may reduce blood sugar: fenugreek, Panax ginseng, Siberian ginseng, guar gum, etc.
  • Herbs and supplements that thin the blood: clove, angelica, garlic, ginkgo biloba, Panax ginseng, turmeric, etc.
  • Xylitol: interaction with this sugar alcohol may cause low blood sugar

Keep L-arginine supplements in a cool, dry area. Avoid exposing the supplement to heat or moisture.

L-arginine is used in pregnancy under certain circumstances, including preeclampsia.

L-arginine supplementation during pregnancy is typically prescribed and monitored by a healthcare provider for a specific reason, such as preeclampsia or the risk of preeclampsia and intrauterine growth restriction (IUGR) (22, 26).

There’s some evidence that L-arginine supplements may improve pregnancy outcomes, as well as fetal and maternal health in women from both high- and low-resource areas.

This is because during pregnancy, the body’s need for L-arginine grows due to fetal development and placental growth. This increased need may not be met through diet, especially in women living in low-resource settings without access to protein-rich foods (27).

Additionally, although the increased demand for arginine during pregnancy can be provided through diet, protein or individual amino acid supplements may be necessary under certain circumstances.

This may include women who follow restrictive diets or are experiencing severe nausea and vomiting during pregnancy, rendering them unable to meet demands through dietary intake.

However, supplements during pregnancy should always be approved and monitored by a healthcare provider. If you are pregnant and interested in taking supplemental L-arginine, consult your healthcare provider for advice.

L-arginine supplements have not been researched in breastfeeding women. For this reason, it’s important to ask your healthcare provider whether taking L-arginine supplements is safe and necessary for your individual needs during breastfeeding.

The safety of L-arginine has been demonstrated in many populations, including pregnant women and older adults. However, some people, including those with conditions that affect the liver or kidneys, should avoid L-arginine (22).

L-arginine supplements are sometimes used in children in the clinical setting and deemed safe when prescribed in appropriate doses. Yet, arginine supplementation in children should always be monitored by a healthcare provider.

It’s not recommended to give your child L-arginine unless it’s medically necessary and was suggested by a healthcare provider.

This advice is extremely important to follow, as giving a child too high a dose of L-arginine may result in serious side effects and can even be fatal (22).

After consumption, your gut and liver rapidly metabolize L-arginine before it has the chance to reach systemic circulation. For this reason, some argue that L-citrulline, a precursor to L-arginine, may be a better choice for increasing arginine levels.

L-citrulline is an amino acid that may be used as an alternative to L-arginine when taken as a supplement.

L-citrulline is a nonessential amino acid that’s a precursor to L-arginine. L-citrulline is converted into L-arginine through a series of enzymatic reactions that take place primarily in your kidneys (28).

Research shows that L-citrulline supplements can raise body levels of L-arginine. In fact, some studies show that L-citrulline is more effective at increasing arginine levels than L-arginine supplements (29, 30, 31, 32, 33).

Research has likewise shown that L-citrulline supplements may offer benefits similar to those of L-arginine supplements.

For example, similarly to L-arginine, L-citrulline has been shown to help reduce blood pressure and improve erectile dysfunction in some studies (34, 35).

Additionally, studies show that when L-citrulline used on its own or in combination with L-arginine, it may improve athletic performance and enhance muscle recovery in athletes (33, 36, 37, 38).

Furthermore, some of these studies found that citrulline supplements may be more effective than L-arginine supplements at enhancing athletic performance (39, 40).

Therefore, athletes may benefit more from L-citrulline or a combination of L-arginine and L-citrulline over L-arginine alone.