Remove the cap by pushing it down and twisting it counter-clockwise. We also looked at additional services, such as access to digital pharmacies and home delivery options. This medicine has been approved in the United States to treat premenopausal females who have low sexual desire. Viagra is not for use by females. Two of the questions from the IIEF served as primary study endpoints; categorical responses were elicited to questions about 1 the ability to achieve erections sufficient for sexual intercourse and 2 the maintenance of erections after penetration. The pharmacokinetics of sildenafil in patients with severely impaired hepatic function Child-Pugh Class C have not been studied [see Dosage and Administration 2. The mechanism of action for ED pills is simple: They inhibit the PDE5 enzyme which regulates the signals responsible for the smooth muscle tissue.Next steps Viagra (sildenafil) is a brand-name oral tablet prescribed for erectile dysfunction. The cost of the drug with and without insurance can depend on several factors, such as . Who may not be able to take sildenafil. Sildenafil is not suitable for some people. To make sure it’s safe for you, speak to your doctor or pharmacist before taking sildenafil if you: have ever had an allergic reaction to sildenafil or any other medicine. have recently had a stroke, heart attack or a heart problem – your doctor should.  · The effects may be increased because of slower removal of the medicine from the body. Leukemia (blood related cancer) or. Multiple myeloma (blood related cancer) or. Sickle-cell anemia (blood disorder)—Sildenafil should be used with caution in these patients as problems with prolonged erection of the penis may occur.