Vardenafil usually works for 4 to 5 hours. This medicine works best when you take it on an empty stomach an hour before sex. This medicine also works best when you take it an hour before sex on an empty stomach. 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. The most common side effects of VIAGRA: headache; flushing; upset stomach; abnormal vision, such as changes in color vision such as having a blue color tinge and blurred vision; stuffy or runny nose; back pain; muscle pain; nausea; dizziness; rash. Oral ED medications are generally well-tolerated, Dr.11 Viagra Alternatives Approved by Doctors. Alternative medications. Side effects. Natural remedies. Other options. Treatment. When to see a doctor. FAQs. Takeaway. Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . Is there an over-the-counter Viagra? Viagra is only available with a prescription in the United States, Canada, and most other countries. Viagra is sold under the generic .