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.

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.

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.

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.