Sexual Dysfunction
Low doses of arginine, at 500 mg three times a day, have not been found to be effective. A double-blind, placebo controlled trial of 50 men with erectile dysfunction tested arginine at a dose of 5 grams per day for six weeks. About a third of the participants who received arginine showed improvement, but that improvement was greater than the 10% improvement seen in the placebo group. Arginine has been studied in combination with other nutrients as a treatment for sexual dysfunction in women. A small trial found some improvement with a combination treatment (ArginMax for Women) providing a daily dose of 2,500 mg of Arginine, as well as ginseng, ginkgo, and damiana. In a four-week, double-blind study, 77 women with decreased libido were given either the combination product or placebo. Those taking the product showed statistically greater improvement such as increased reported sexual desire in 71% of participants given the treatment versus 42% in the placebo group. Other improvements were relative satisfaction with sex life and improved clitoral sensation. No significant side effects were seen in either group.

A study done at the University of Texas at Austin examined the effects of arginine combined with yohimbine on sexual arousal in postmenopausal women. Twenty-four women participated in three treatment sessions in which sexual responses to erotic stimuli were measured following treatment with either arginine glutamate (6 g) plus yohimbine (6 mg), yohimbine alone (6 mg), or placebo, using a randomized, double-blind design. Sexual responses were measured at one hour after taking the supplements. Compared to placebo, the combined oral administration of arginine and yohimbine substantially increased vaginal pulse amplitude responses to the erotic film

Interestingly, a similar study using the same combination was tested at the Hopital Foch, Suresnes, in France. But this time, the study was done with men who had erectile dysfunction (ED). Forty-five patients were included in this study. During each of the 2-week, crossover periods, the supplements were administered orally, two hours before intended sexual intercourse. This pilot study showed that the oral administration of the arginine and yohimbine combination is effective in improving ED.

Additional Potential Benefits
A Japanese study shows arginine supplementation improves renal function in patients with chronic heart failure. Polish researchers have found that arginine supplementation increases exercise tolerance in stable coronary artery disease patients.

Arginine has also been tested in those with hypertension. This amino acid is able to dilate vessels and lower blood pressure, but it appears that the effects are not long lasting. The proper therapy of hypertension requires that a nutrient or medicine have a long lasting effect.

Mechanism of Action
The most likely explanation for the modest effectiveness of arginine is its conversion into nitric oxide. Nitric oxide is converted into cGMP, which becomes the secondary messenger that causes smooth muscle relaxation, resulting in more blood going into organs and tissues. However, nitric oxide is metabolized quite rapidly, which may explain why taking arginine does not lead to consistent or prolonged erections.