Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take. Viagra can be taken as long as four hours or as little as 30 minutes before sex. Viagra generally only stays in your system for four to six hours. 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. Oral medicines for ED usually work well and cause few side effects.Sildenafil (Viagra) and tadalafil (Cialis) are the most commonly prescribed medications for ED, and they have the longest track record. For occasional use, most people start with sildenafil. For regular use, tadalafil can be a better fit. Some people prefer to . Viagra, Cialis, Levitra, and Stendra are oral medications used to treat erectile dysfunction (ED). You may also know them by their generic names: sildenafil (Viagra) tadalafil (Cialis). Tadalafil (Cialis) Switch to brand medication info_outlined Used for Benign Prostatic Hyperplasia and Erectile Dysfunction MORE expand_more Check your prescription Prescription 5mg tadalafil (Cialis) (30 tablets) edit Choose your pharmacy moses lake, .