What It Is:
L-arginine, also referred to as arginine, is required to carry out the synthesis of nitric oxide, a compound that, working through cGMP, relaxes blood vessels and allows more blood to flow through arteries. It has been hypothesized that taking extra arginine will increase nitric oxide levels and, in turn, increase blood flow to various parts of the body.

What It Does: (See the CL Encyclopedia article on Arginine for more details)
Note: The first three conditions in this section are life-threatening. If you have angina, congestive heart failure, or intermittent claudication, do not attempt to treat yourself with arginine except under physician's supervision.

Congestive Heart Failure (fluid build-up in lungs and legs due to heart weakness)
Several small clinical trials have shown that arginine at doses of 5 grams to 15 grams (1 gram = 1,000 mg) daily may improve symptoms of congestive heart failure as well as objective measures of heart function (Hambrecht, J Am Coll Cardiol 2000).

Angina (chest pain due to reduce blood flow to heart)
Studies have shown improvement in exercise tolerance, although not heart function, in people with angina when taking 6 grams per day of arginine. (Bednarz Int J Cardiol 2000). Another study showed decreased symptoms of angina when 6.6 grams of arginine was taken daily (from a fortified food bar with vitamins and minerals) (Maxwell, J Am Coll Cardiol 2002).

Intermittent Claudication (leg pain during exercise due to insufficient blood flow)
A study showed that 2 weeks of treatment with 6.6 grams of arginine daily (from a fortified food bar with vitamins and minerals) improved walking distance by 66% (Maxwell, Vasc Med 2000). However, a longer (6-month) and better designed study (Wilson, Circulation 2007) found arginine (3 grams per day) to be less effective than placebo.

Raynaud's phenomenon
Because L-arginine is involved in the synthesis of nitric oxide (a compound which relaxed blood vessels and allows more blood to flow through them), it is sometimes promoted for this use. A few case reports (Rembold, Mol Cell Biochem 2003) and preliminary studies have suggested a benefit in certain people. For example, one very small study found that a dose of 4 grams of L-arginine taken twice daily was helpful for Raynaud's phenomenon associated with systemic sclerosis, but not for primary Raynaud's phenomenon (not caused by another disease/condition); however, this study did not include a placebo, so it's not possible to determine whether L-arginine was truly effective (Agostoni, Int J Clin Lab Res 1991). A study (noted in the Encyclopedia article about Raynaud's phenomenon) which used the same dose of L-arginine and did include a placebo found no benefit for primary Raynaud's phenomenon (Khan, Arthritis Rheum 1997).

Sexual Enhancement (See Product Review of Sexual Enhancement Supplements for more information)
Arginine might offer modest benefit for sexual dysfunction in men. Although arginine alone has not been studied as a treatment for sexual dysfunction in women, a small but reasonably good double-blind trial found evidence for benefit with a combination formula (ArginMax for Women) providing a daily dose of 2,500 mg of L-arginine, as well as amounts of herbs and numerous vitamins and minerals

Cancer
If a person with cancer is malnourished, L-arginine may improve immune function as well as long-term survival, as shown in a study of people after cancer surgery given arginine by feeding tube (Zhao, J Cancer Res Clin Oncol 2013). However, in people who are not malnourished, the evidence of benefit from taking L-arginine is mixed.

In women with breast cancer, 30 grams of L-arginine taken for 3 days prior to chemotherapy did not improve the response rate to the treatment compared to women who received a placebo -- although it did improve the response rate in the subset of women whose tumors were smaller than 6 cm (88% vs 52% with placebo, respectively) (Heys, Int J Oncol 1998). The same dose has significantly improved certain immune responses in women with breast cancer (Brittenden, Surgery 1994) and slowed tumor activity in people with non-cancerous colorectal tumors and decreased a marker of tumor progression in people with cancerous colorectal tumors (Ma, Clin Cancer Res 2007).

Be aware that certain types of cancer are especially dependent on arginine to grow — including melanoma and hepatocellular carcinoma -- and drug treatments that help to break down and eliminate arginine are being investigated as treatments (Phillips, Cancer Res Treat 2013). For people with these types of cancers, arginine supplementation would not seem advisable.

Other Uses
L-arginine may modestly increase exercise endurance in recreational and older athletes, although not in trained athletes. It is widely promoted as a key ingredient in "nitric oxide" supplements, which are touted as increasing muscle size, but clinical evidence does not support this use. (See the Nitric Oxide Supplements Review Article for more information.) 

 

Some evidence suggests that arginine may be helpful in AIDS-related wasting, colds, necrotizing enterocolitis, intolerance to nitrate medication, post-surgery recovery and in improving kidney function in kidney transplant patients treated with cyclosporine. There is also preliminary evidence of a role for arginine in other treating conditions, including senile dementia, hypertension, and sickle cell disease.

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