Medical consultations were also taken into consideration, as PDE5 inhibitors require a valid prescription from a licensed medical provider. The mechanism of action for ED pills is simple: They inhibit the PDE5 enzyme which regulates the signals responsible for the smooth muscle tissue. How we source info. Sildenafil is an on-demand pill that lasts for up to five hours. The generic versions are just as effective and much less expensive. Erectile dysfunction medications require a prescription from a licensed provider.Price without insurance: starts at $80 per dose. Doses: 25, 50, and milligrams (mg) Supply: 30 or 90 days. To get a prescription for Viagra through the Optum Store, you’ll . Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online. SILDENAFIL – ORAL (sil-DEN-a-fil) COMMON BRAND NAME(S): Viagra. USES: Sildenafil is used to treat male sexual function problems (impotence or erectile .