L-arginine

Overview

L-arginine is an amino acid that helps the body build protein.

Your body usually makes all the L-arginine it needs. L-arginine is also found in most protein-rich foods, including fish, red meat, poultry, soy, whole grains, beans and dairy products.

As a supplement, L-arginine can be used orally and topically. It can also be administered intravenously (IV).

Because L-arginine acts as a vasodilator, opening (dilating) blood vessels, many people take oral L-arginine to treat heart conditions and erectile dysfunction.

What the research says

Research on the use of L-arginine for specific conditions shows:

Angina. Studies suggest that L-arginine might decrease symptoms and improve quality of life in people with a mild to severe form of this type of chest pain.
High blood pressure (hypertension). Some research has shown that oral L-arginine can lower blood pressure in healthy people, people with mild blood pressure elevation and diabetes, and in people with a type of high blood pressure that affects the arteries in the lungs and the right side of the heart (pulmonary hypertension). Infusions of L-arginine also appear to lower blood pressure in people with hypertension.
High blood pressure during pregnancy. Some studies show that L-arginine infusions may lower blood pressure in pregnant women who develop high blood pressure.
Preeclampsia. L-arginine infusions may lower blood pressure in women with this pregnancy complication. Some research shows that taking oral L-arginine might help prevent preeclampsia in pregnant women.
Erectile dysfunction. Taking oral L-arginine might improve sexual function in men with erectile dysfunction due to a physical cause.
Peripheral arterial disease (PAD). When taken orally or by infusion for a short period of time, L-arginine may improve symptoms and blood flow in people with this circulatory condition.

Our take

Generally safe

L-arginine is considered to be generally safe. It might be effective at lowering blood pressure, reducing the symptoms of angina and PAD, and treating erectile dysfunction due to a physical cause.

However, if you take a blood pressure drug, talk to your doctor before using L-arginine.

Safety and side effects

Using L-arginine orally or topically is generally considered safe.

Oral use of L-arginine might cause:

Nausea, abdominal pain and diarrhea
Bloating
Gout
Headache
Allergic response
Airway inflammation or worsening of asthma symptoms

L-arginine isn't recommended for people who have had a recent heart attack due to concerns that the supplement might increase the risk of death.

L-arginine can worsen allergies or asthma. Use the supplement with caution if you have these conditions.

Be careful about taking L-arginine if you've had cold sores or genital herpes. Too much L-arginine in your system can potentially trigger the virus that causes those conditions.

Interactions

Possible interactions include:

Anticoagulants and anti-platelet drugs, herbs and supplements. These types of drugs, herbs and supplements reduce blood clotting. Taking L-arginine with them might increase the risk of bleeding.
Blood pressure drugs, herbs and supplements. L-arginine might lower blood pressure in people who have high blood pressure. Combining use of L-arginine with a blood pressure drug, herb or supplement might increase the risk of blood pressure becoming too low.
Diabetes drugs, herbs and supplements. L-arginine might decrease blood sugar levels in people with diabetes. If you're taking diabetes drugs, herbs or supplements, your dosage might need to be adjusted.
Isoproterenol (Isuprel). Use of this heart medication with L-arginine might cause your blood pressure to become too low.
Nitrates. Use of this chest pain medication with L-arginine might cause your blood pressure to become too low.
Water pills (potassium-sparing diuretics). Don't take L-arginine with amiloride (Midamor), spironolactone (Aldactone, Carospir) or triamterene (Dyrenium). These medications can increase potassium levels, increasing the risk of developing a higher than normal level of potassium in your blood (hyperkalemia).
Sildenafil (Revatio, Viagra). Use of this erectile dysfunction medication with L-arginine might cause your blood pressure to become too low.