L-arginine is a naturally occurring amino acid that's found in food. It also plays a role in several bodily functions, such as making protein.
L-arginine also affects the release of growth hormones, insulin, and other substances in your body. Your body may also convert L-arginine to a chemical called nitric oxide, which widens blood vessels and improves blood flow.
The human-made version of L-arginine is thought to work similarly to the natural amino acid in your body.
This article discusses what you should know about L-arginine—its potential uses, side effects, and interactions.
Dietary supplements are not regulated the way drugs are in the United States, meaning the Food and Drug Administration (FDA) does not approve them for safety and effectiveness before products are marketed. When possible, choose a supplement tested by a trusted third party, such as U.S. Pharmacopeia, (USP), ConsumerLab.com, or NSF International.
However, even if supplements are third-party tested, they are not necessarily safe for all or effective in general. Therefore, talking to your healthcare provider about any supplements you plan to take and asking about potential interactions with other supplements or medications is essential.
- Active ingredients (s): L-arginine
- Alternative name(s): Arginine, Arg, (2S)-2-amino-5-(diaminomethylideneamino) pentanoic acid
- Legal status: Legal in most U.S. states
- Suggested dose: May vary based on the dosage form and medical condition
- Safety considerations: Likely safe (short-term use)—even in pregnancy and children; limited data on breastfeeding; may be harmful to people with certain medical conditions and interact with some prescription medications
Uses of L-Arginine
Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.
As with many natural products, L-arginine is used for various reasons.
Several studies have assessed L-arginine for the following potential uses.
Metabolic Conditions and Heart Disease
L-arginine might provide some value to people with metabolic conditions (e.g., high blood sugar and excess weight) and heart disease.
But it's unclear how effective L-arginine is because of the variability (important differences) between previous clinical trials.
For example, there were different L-arginine dosage forms among studies. And there were differences in the L-arginine dosages (amounts or strengths) and the length of therapy.
For these reasons, researchers conducted a systematic review and meta-analysis (analytical review of a collection of studies) to more clearly understand L-arginine's benefits.
According to research, L-arginine might improve blood flow in select groups of people. It may increase nitric oxide levels in people with metabolic conditions and heart disease. However, the results were unclear in the studies reviewed.
Further research with higher-quality clinical trials is still necessary—especially since there is a concern that L-arginine might cause more harm in people with a recent heart attack.
Postpartum hypertension is a condition of high blood pressure after giving birth. A systematic review found insufficient data to make clear conclusions about L-arginine's benefits and risks for this condition.
Further high-quality clinical trials with additional data are still needed.
According to the National Library of Medicine (NLM), L-arginine is possibly effective for erectile dysfunction (ED).
A review also suggested that people with ED might benefit from L-arginine alone or in combination with other medications. But additional research with larger and higher-quality studies is still warranted.
In a systematic review, people assigned female at birth who were experiencing fertility problems benefited from antioxidants—like L-arginine.
These antioxidants didn't seem to increase the risk of digestive system-related side effects, miscarriages, multiple births, or ectopic pregnancies.
While this looks promising, the results are from studies considered to be of low quality. For this reason, more high-quality clinical trials are necessary to better evaluate the effects and safety of L-arginine's use for fertility problems.
What Are the Side Effects of L-Arginine?
As with many medications and natural products, side effects are possible with L-arginine.
Common Side Effects
In general, short-term use of L-arginine is likely safe in various dosage forms for most people, but there are potential side effects.
For example, when taken by mouth, common side effects may include:
- Low blood pressure
- Stomach pain
Severe Side Effects
While L-arginine is safe for most people, there's a chance of severe side effects in some people, as follows:
- Severe allergic reaction: A severe allergic reaction is a possible serious side effect of any medication. Symptoms may include breathing difficulties, itchiness, and rash.
- Risk of death with a recent heart attack: L-arginine may raise the risk of death after a recent heart attack—especially in older adults.
- Abnormal heart rhythm: In people with kidney problems, L-arginine may raise potassium levels, leading to an abnormal heart rhythm.
- Blood pressure problems: During and after surgery, L-arginine might make it harder to control your blood pressure. For this reason, it might be necessary to stop taking L-arginine two weeks before your procedure.
- Tumor growth: L-arginine may promote the growth of certain tumors.
- Abnormal white blood cell (WBC) count: L-arginine may raise the levels of certain WBCs.
If you're having a severe allergic reaction or if any of your symptoms feel life-threatening, call 911 and get medical help right away.
L-arginine may pose risks in the following situations:
- Severe allergic reaction: Avoid L-arginine if you have a severe allergic reaction to it or its components (parts or ingredients).
- Pregnancy: When taken by mouth, short-term use of L-arginine is likely safe during pregnancy. But it's unknown about the effects and safety of long-term L-arginine on pregnant people and the fetus. If you're considering taking L-arginine, talk with your healthcare provider about the benefits and risks of L-arginine during pregnancy.
- Breastfeeding: There isn't enough information to assess the effects and safety of L-arginine on nursing babies. If you want to take L-arginine, discuss with your healthcare provider about the benefits and harms of L-arginine while breastfeeding.
- Children: L-arginine is likely safe in children orally (by mouth), as a toothpaste, or as an inhaled form. If you're considering L-arginine for your child, talk with your child's healthcare provider (pediatrician) first. They will help you weigh the benefits and risks of L-arginine for your child.
- Older adults over 65 years of age: Some older adults may be more sensitive to medication side effects, particularly those who've had a recent heart attack. For this reason, speak with your healthcare provider before trying L-arginine.
- Recent heart attack: L-arginine might raise the risk of death in people with a recent heart attack—especially in older adults. So, your healthcare provider is unlikely to recommend L-arginine if you have a recent heart attack.
- Abnormal heart rhythm: L-arginine may raise potassium levels, especially in people with kidney problems. And these abnormal potassium levels may result in an abnormal heart rhythm. Your healthcare provider may recommend avoiding L-arginine if you have an abnormal heart rhythm condition.
- Kidney problems: In people with kidney problems, L-arginine may increase potassium levels, leading to an abnormal heart rhythm. If you already have kidney problems, your healthcare provider may recommend avoiding L-arginine.
- Blood pressure problems: L-arginine might make it hard to control your blood pressure, especially during and after surgery. For this reason, your healthcare provider may closely monitor you—if you already have blood pressure problems. Your healthcare provider may also want to stop L-arginine a few weeks before your procedure.
- Tumors: L-arginine might promote the growth of certain tumors. For this reason, your healthcare provider may want to monitor you or recommend against L-arginine closely—if you have cancer.
- Abnormal white blood cell count: L-arginine may raise your WBC count. So, your healthcare provider may want to closely monitor you and your WBC levels—if you're taking L-arginine.
Dosage: How Much L-Arginine Should I Take?
Always speak with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs.
While there are some human studies on L-arginine, high-quality clinical trials are still necessary.
For this reason, there are no guidelines on the appropriate dosage to take L-arginine for any condition. If you take L-arginine, follow your healthcare provider's suggestions and product label instructions.
What Happens If I Take Too Much L-Arginine?
There is little information about L-arginine toxicity and overdoses in humans. But generally, L-arginine seems safe with short-term use of up to 20 grams (g) daily.
Overdoses with L-arginine, however, might be similar to its potential common or severe side effects, which might be exaggerated or excessive.
High doses of L-arginine might promote tumor growth, plus large amounts of L-arginine may also increase the levels of specific white blood cells. But longer and higher-quality clinical trials are still needed to assess L-arginine's safety in humans better.
Use caution when taking L-arginine with the following:
- Blood pressure medications: L-arginine may lower your blood pressure. This may result in additive effects with your blood pressure medications. If your blood pressure is too low, you might experience dizziness and fainting spells. Examples of blood pressure medications include Zestril (lisinopril) and Diovan (valsartan).
- Blood thinners: L-arginine may slow down your blood clotting time. So, combining L-arginine with blood thinners may result in worsening bruising and bleeding side effects. Jantoven (warfarin) is an example of a blood thinner.
- Certain diuretics (water pills): L-arginine may raise your potassium levels, and certain water pills—like Aldactone (spironolactone)—can also do this. So, combining these medications might result in excessively high potassium levels, leading to an abnormal heart rhythm.
- Diabetes medications: L-arginine may lower your blood sugar. This might have additive effects on your diabetes medications, such as insulin. If your blood sugar is too low, symptoms may include tremors and sweating.
- Erectile dysfunction (ED) medications: L-arginine might be used for ED. And L-arginine may lower your blood pressure, similar to several ED medications, such as Viagra (sildenafil). For this reason, taking these medications together might result in excessively low blood pressure.
It is essential to carefully read a supplement's ingredients list and nutrition facts panel to learn which ingredients and how much of each ingredient is included. Please review this supplement label with your healthcare provider to discuss potential interactions with foods, other supplements, and medications.
How to Store L-Arginine
Since storage instructions may vary by product, carefully read the directions and packaging label on the container.
Keep your medications tightly closed and out of the sight and reach of children and pets, ideally locked in a cabinet or closet. Store your medications in a cool and dry place.
Discard after one year or as indicated on the packaging. Avoid putting unused and expired drugs down the drain or in the toilet.
Visit the FDA's website to know where and how to discard all unused and expired drugs. You can also find disposal boxes in your area.
Ask your pharmacist or healthcare provider if you have any questions about the best ways to dispose of your medications or supplements.
L-arginine is a naturally occurring amino acid that may be converted to a chemical called nitric oxide. And like L-arginine, nitric oxide is also available as a human-made version.
For these reasons, nitric oxide is likely the most similar natural medication to L-arginine.
Frequently Asked Questions
What is the most common dosage form of L-arginine?
L-arginine is available in many dosage forms—with powder likely being the most common.
Is L-arginine available from manufacturers in the United States?
Yes. There are L-arginine products manufactured in the United States.
How do I take L-arginine safely?
In general, to safely take natural medications—like L-arginine—inform your healthcare providers and pharmacists about any medication changes. This includes over-the-counter (OTC), herbal, natural medications, and supplements.
They can help prevent possible interactions and side effects. They can also ensure you’re giving L-arginine a good trial at appropriate doses.
Sources of L-Arginine & What to Look For
There are several different sources of L-arginine.
Food Sources of L-Arginine
L-arginine is a naturally occurring amino acid that's found in food.
Some foods that contain L-arginine are:
- Dairy products
- Red meat
L-arginine is available in a variety of forms, including capsules and tablets. If you have difficulties swallowing pills, L-arginine might also be available in other dosage forms, such as liquid and powder.
L-arginine may also be available in inhalation, intravenous (into the vein), toothpaste, and topical (e.g., cream and gel). There may also be vegan and vegetarian options.
What works for you will depend on your preference and what you hope to get regarding effects. Each product may work a bit differently, depending on the form. So, following your healthcare provider's recommendations or label directions is essential.
L-arginine is a naturally occurring amino acid that's found in food. L-arginine may have potential uses for metabolic conditions (e.g., high blood sugar and excess weight), heart disease, postpartum hypertension (high blood pressure after childbirth), erectile dysfunction (ED), and fertility problems. In general, short-term use of L-arginine seems safe.
But as with many medications and natural products, side effects and medication interactions are still possible. High-quality, long-term clinical trials are still necessary to evaluate L-arginine's effectiveness and safety.
Before taking L-arginine, contact your registered dietitian nutritionist, pharmacist, or healthcare provider to help you safely achieve your nutrition and health goals.