Taking L-arginine as a supplement may increase blood flow and muscle growth. For some, it may also cause side effects, such as nausea or diarrhea.

L-arginine is one of the amino acids the body needs to build muscle and heal wounds. The body can produce L-arginine, and people can also get it in their diet.

Occasionally, a person’s need for L-arginine may exceed their body’s ability to synthesize it naturally. In these cases, doctors may prescribe L-arginine in the form of oral medications, injections, or creams.

Keep reading to learn more about the potential therapeutic benefits of L-arginine and the research behind them.

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L-arginine has two main effects: it turns into nitric oxide, and it helps the body build protein.

Nitric oxide is involved in the dilation of blood vessels. Having enough helps blood vessels open up, increasing blood flow.

Improved blood flow can result in more oxygen and nutrients reaching the muscles, and may help the body to remove waste products, such as lactate and ammonia, from those muscles more quickly.

There are many other claims about the health benefits of L-arginine, but not all of them have support from scientific studies.

Some of the potential benefits that do have evidence include:

  • Improving athletic performance: The results of a 2020 review and meta-analysis suggest that L-arginine supplements may have a positive effect on aerobic and anaerobic exercise performance when a person takes them 60 to 90 minutes prior.
  • Reducing high blood pressure: A 2021 meta-analysis suggests L-arginine may help to reduce high blood pressure. This appears to work more effectively in females than in males.
  • Delaying type 2 diabetes: A 2017 study tested L-arginine supplementation in middle aged adults with metabolic syndrome and impaired glucose tolerance. The authors found that the supplement may help to delay the onset of diabetes for “a long period”.
  • Treating peripheral arterial disease (PAD): Because of L-arginine’s effects in widening blood vessels, it may help those with PAD. A small study found that L-arginine infusion improved the function of narrowed blood vessels, but more research is necessary.
  • Treating pregnancy complications: A 2021 review of 45 previous studies found that L-arginine may help to to reduce preeclampsia or gestational hypertension during pregnancy.
  • Preventing necrotizing enterocolitis: L-arginine may help prevent necrotizing enterocolitis, a serious illness in premature infants, according to a 2017 study.

More research is necessary to evaluate L-arginine’s potential to heal wounds faster or improve breathing in people with illnesses affecting the respiratory system.

People can get L-arginine as part of their regular diet. Some people take L-arginine as a supplement. However, as with any supplement, a person should talk to a doctor before use.

While L-arginine supplements may have some benefits, they can sometimes cause side effects, such as nausea or diarrhea.

In certain situations L-arginine may also result in some more serious effects, such as:

  • reduced blood pressure, which may be a problem for people who already have low blood pressure
  • interactions with certain medications
  • increasing the growth of specific types of tumor
  • potential kidney damage with long-term use, although more research in humans is necessary to confirm this

Always consult a doctor or dietitian before taking any new dietary supplement.

According to the National Institutes of Health (NIH), L-arginine doses of up to 9 grams (g) per day are usually safe for several weeks, but larger doses may cause adverse effects.

Additionally, the effects of long-term L-arginine supplementation are not clear in humans.

The dosage that is beneficial for a person may depend on their age, existing health conditions, and the reason for supplementation.

The Food and Drug Administration (FDA) does not check the safety or effectiveness of dietary supplements, so it is important to choose a reputable brand that undertakes third-party testing to prove the purity and quality of their products.

L-arginine supplements and medications may interact with drugs that lower blood pressure, including sildenafil (Viagra).

It may also enhance the effects of some medications, which could result in adverse effects.

People who take medications or have pre-existing health conditions should consult a doctor before taking additional L-arginine.

Many people can get enough L-arginine through a balanced diet. Food sources include animal products, such as:

  • meat
  • seafood
  • eggs

Plant-based sources include:

  • nuts
  • seeds
  • soy protein
  • watermelon

Food sources alone may not provide enough L-arginine to meet a person’s needs in some cases. Getting more foods rich in protein may help, but if this is not possible, people can speak with a doctor or dietitian for tailored advice.

L-arginine is an amino acid that the body needs to function properly. A person can obtain it through the diet by consuming animal proteins and some plant-based proteins.

Taking L-arginine supplements may support muscle growth, improve athletic performance, lower blood pressure, and even prevent some medical conditions.

However, the effects of supplementing long-term are unknown, and high doses could have risks. There are also some people who may need to avoid L-arginine. As a result, it is best to talk with a doctor before taking L-arginine.