In 1998, with the development of an oral drug for erectile dysfunction (ED) called sildenafil, a major change began in the field of ED treatment. The drug's mechanism of action is based on the inhibition of the phosphorylation ester hydrolase type 5 (PDE5) corpus cavernosum smooth muscle cells. The effect of sildenafil is very satisfactory, and many studies have reported that its effect in improving ED is significant. In Korea, it has been widely used as a first-line treatment for patients with ED. Patent rights for this type started to expire in 2012, and generic versions of this drug have been available since 2015. Currently, more than 100 types of generic drugs are available in Korea. Unfortunately, there are many product names, but looking at the components, the PDE5 inhibitors available in Korea include sildenafil, tadalafil, valdenafil, udenafil, mirodenafil, and avanafil. As treatment methods using PDE5 inhibitors have been further developed, a few therapies have been announced, including daily dosing regimens and combinations with existing therapies. Several different types of drug are now on the market, including film, granular, and jelly forms, which provide a variety of therapeutic options. As more studies of sexual dysfunction not only in men but also in women have been conducted, some positive treatment effects have been reported. In addition to ED, use of PDE5 inhibitors is being studied as a treatment for other conditions such as Alzheimer's disease, heart disease, and infertility. This paper briefly discusses the mechanism of action, side effects, various dosage methods, combined use of oral ED drugs, and the effects of these therapeutic agents for other diseases.