L-arginine (el-AHR-jih-nene) is an organic substance called an amino acid. Most often, your body makes all the L-arginine it needs. You also can get L-arginine through your diet in foods such as nuts, fish, red meat, soy, whole grains, beans and dairy products.

The body changes L-arginine to nitric oxide, a substance known to widen blood vessels. Some people take L-arginine supplements to relax and open arteries, which might help lower blood pressure. But L-arginine supplements are rarely needed. They may be more likely to benefit people who have too little of this amino acid. And because they can affect how some medicines work and worsen certain health conditions, they shouldn't be taken unless a healthcare professional recommends them.

Research on L-arginine has shown mixed results. The most recent research suggests that L-arginine may help lower blood pressure. It also may help people who have a type of high blood pressure that affects the arteries in the lungs and the right side of the heart. This is called pulmonary hypertension. The benefits for pulmonary hypertension have been shown in people who also have a disease of the red blood cells called sickle cell disease.

Some studies also suggest that short-term use of L-arginine infusions may lower high blood pressure during pregnancy. Infusions are given through a vein. L-arginine given by mouth or as an infusion is likely to be safe during pregnancy when used short term during the second and third trimesters.

One large review of studies looked at data on adults who took daily L-arginine supplements. Some of the adults had high blood pressure, and some did not. Overall, the adults lowered their bottom blood pressure number, called the diastolic pressure, by about 2.6 millimeters of mercury (mm Hg). And they lowered their top blood pressure number, called the systolic pressure, by about 6.4 mm Hg. The researchers linked the benefits with taking less than 9 grams of L-arginine a day for 4 to 24 days. But more research is needed to assess the effects of taking this supplement long-term.

When it comes to heart health, L-arginine may work better when combined with other vitamins, such as vitamins B-6 and B-12. But larger, more robust studies are needed to confirm these findings before experts can recommend everyday use of these supplements.

L-arginine-medicine interactions

It's important to know that L-arginine supplements can affect the way some medicines work, such as:

• Blood thinners, including aspirin and warfarin (Jantoven).
• Certain diuretics.
• Nitroglycerin (Nitro-dur, Nitromist, Nitrostat, others).
• Some high blood pressure medicines.
• Erectile dysfunction medicines.
• Diabetes medicines.

Who shouldn't take L-arginine

Don't take L-arginine if you've had a heart attack. There are concerns that the supplement might raise the risk of death.

L-arginine supplements can make allergies and asthma worse. Use with caution.

Don't take L-arginine supplements if you've had cold sores or genital herpes. Too much L-arginine in your system can make the virus that causes those conditions become active again.

Also, don't take L-arginine if you have kidney disease. It may disturb the balance of important minerals in the body called electrolytes. Use of L-arginine has also caused deadly irregular heart rhythms in some people who have problems with kidney function or kidney failure.

If you're scheduled to get surgery, tell your healthcare professional if you take L-arginine. You'll likely be told to stop taking the supplement at least two weeks before your procedure.

Talk to your healthcare professional about supplements

A healthy diet and regular exercise are among the best ways to keep your blood pressure healthy. If you're thinking about taking an herbal or dietary supplement, such as L-arginine, talk with your healthcare professional first. Some supplements can affect how blood pressure medicines work or make certain health conditions worse.