These medicines are called PDE5 inhibitors. Psychological factors like stress, depression, or anxiety can also contribute. Side effects Side effects of oral ED medicines are often mild. Popular ED medications found online include: Viagra sildenafil : As the first FDA-approved PDE5 inhibitor for ED, sildenafil is taken 30 minutes to four hours before sexual intercourse to help achieve and maintain an erection. Make sure to get an estimate of when you can expect your prescription in the mail.Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. Most popular Safeway $ retail Save 94% $ Get free savings Low price Walgreens $ retail Save 94% $ Get free savings directions Closest store Rite Aid. Most popular Low price Walmart $ retail Save 99% $ One-time offer Get free savings Walgreens $1, retail Save 99%.