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L-arginine pills stimulate nitric oxide production.

Nitric oxide, or NO, supplements have been marketed as performance enhancers that increase the intensity of your workout, promote oxygen delivery to your muscles, and improve your muscle building capacity, according to the book "Anabolic Primer." These supplements contain L-arginine or L-arginine alpha-ketoglutarate -- which is made up of the amino acid L-arginine and alpha-ketoglutaric acid -- and act as an hemodilator, stimulating the smooth muscle endothelial cells that line the inside of your blood vessels to release nitric oxide. Nitric oxide stimulates vasodilation, or an increase in the diameter of your blood vessels, increasing blood flow to your muscles during exercise. Some side effects are associated with nitric oxide supplements. Consult your physician before using any supplement that stimulates nitric oxide release.


According to, supplementation with L-arginine for the purpose of increasing nitric oxide is generally well-tolerated by most people when taken within the manufacturers recommended guidelines in studies lasting up to six months. However, L-arginine supplementation may result in serious adverse reactions in some people. Arginine supplementation is not recommended for individuals under 18 years old because there is not enough scientific evidence to support its safety.

Allergic Reaction

Although rare, some individuals may experience an allergic reaction to arginine supplementation resulting in a rapid, dramatic increase in histamine production. Histamine is released by your body in response to the perception of the introduction of a toxin to your blood stream, and synthetic L-arginine may be mistaken by your body's immune system as an intruder. According to "Nutrition for Health, Fitness, and Sport," an allergic reaction to nitric oxide supplements may result in swelling of your face, throat, and neck, the appearance of hives, difficulty breathing, and a rapid heartbeat.

Other Side Effects

L-arginine supplementation can lead to several potentially serious side effects in addition to an allergic reaction. In some users, arginine supplementation may cause stomach discomfort, including nausea, stomach cramps, or increased bowel movements. Arginine may also worsen the symptoms of asthma and lower blood pressure. L-arginine may increase the risk of bleeding, blood sugar levels, potassium levels, and can worsen the symptoms of sickle cell disease.

Possible Interactions

According to the National Library of Medicine, L-arginine supplements may interfere with the function and absorption of some medications. If you are taking anti-hypertensive drugs for blood pressure, or nitrates for blood flow to the heart, you should consult your physician before taking a nitric oxide supplement containing L-arginine because serious side effects may occur. L-arginine may also increase the likelihood of experiencing side effects when taken with Viagra or xylitol.

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