Viagra is a sexual function improvement drug, its main active ingredient is sildenafil citrate, which can be used to treat male erectile dysfunction. Viagra is a specific phosphodiesterase inhibitor, and its main mechanism of action is to inhibit the effect of phosphodiesterase, thereby relaxing the smooth muscle in the corpus cavernosum of the penis and allowing more blood to flow into the penis, which in turn enables the penis to become erect and improve sexual dysfunction. It is generally recommended that patients take Viagra under the premise of sexual stimulation, 0.5-1h before sex, the effect is better, if there is no sexual stimulation, then Viagra can not play a therapeutic role. It should also be noted that Viagra will reduce blood pressure, so patients taking nitrate drugs need to be careful to use.