Both men and women report that L-Arginine seems to increase their libido or desire for sex, and some also report that L-Arginine gives them greater endurance and stronger, more powerful orgasms. L-Arginine is a precursor of nitric oxide (NO), a compound whose primary function is to dilate blood vessels in the human body. In men, L-arginine improves blood flow to the genital area and increases penile erection. In women, higher blood flow makes clitoral and vaginal tissues more sensitive and responsive to sexual stimulation. L-arginine also increases muscle mass and reduces belly fat.