Those with a history of blood pressure or heart issues, hormonal imbalances, mental health issues, and diabetes should consult their doctor before trying PDE5 inhibitors. All of the women were taking antidepressants and agreed to be part of a unique trial involving Viagra, in which it would test if the drug could be released earlier due to unspecified “certain circumstances. The mechanism of action for ED pills is simple: They inhibit the PDE5 enzyme which regulates the signals responsible for the smooth muscle tissue. These medicines all work well for ED. When taken at the correct time and paired with sexual stimulation, the erection lasts long enough for successful intercourse. A: Because it is the lowest amount of active ingredient that works for the most patients roughly 80 percent in clinical trials , doctors recommend starting with a dose of 50 mg and get no results, you might want to try increasing the dose to mg. Secure and Anonymous!avanafil (Stendra) About 30 million men in the United States occasionally have a problem with getting or keeping an erection, according to the Urology Care . Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes .