You may opt-out of email communications at any time by clicking on the unsubscribe link in the e-mail. This includes prescription or nonprescription over-the-counter [OTC] medicines and herbal or vitamin supplements. Some people may also have ringing in their ears tinnitus or dizziness. Precautions It is important that you tell all of your doctors that you take sildenafil. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse.Generic name: sildenafil (oral) [ sil-DEN-a-fil ] Brand names: Revatio, Viagra Drug class: Impotence agents Medically reviewed by Sophia Entringer, PharmD. Last updated on . The highest recommended Viagra dose for treating erectile dysfunction (ED) is mg per day, according to the drug’s manufacturer. Doses of mg or mg would be . FAQs What to consider Cost Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. .