Still, there are 32 complaints about Teladoc listed on the site, with over 50 percent of reviewers stating an issue with the product or service. Its availability, ease of use, contents, and legal weight make the PI the resource that should often be the starting point when initiating a search for drug information. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Sildenafil Viagra. The modifications to the PI format were made through FDA research and after consultation with healthcare professionals.Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. This boosts blood flow and helps you get an erection from sexual activity. How oral medicines differ. Instead, when it comes to prescription drugs, the manufacturer’s duty is to provide prescribing physicians with information about the proper use and risks of the product so that the prescriber is then better equipped to educate the consumer/patient about the drug’s use and risks;. The recommended dosage of Viagra for erectile dysfunction (ED) is 50 mg, taken as needed about 1 hour before sexual activity. You can take it 30 minutes to 4 hours before sexual activity.