If you don’t have any health insurance, consider purchasing a plan. Kidney disease that needs to be treated with dialysis. When did your erectile dysfunction start? Generic versions of sildenafil, vardenafil and tadalafil are available. You should also ask what results should expect from using the medication. The information provided is for educational purposes only and is not intended to replace discussions with a healthcare provider. · Viagra is usually taken only when needed, 30 minutes to 1 hour before sexual activity. You may take it up to 4 hours before sexual activity. Stop taking sildenafil and . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects often last for 4 to 5 hours. It might work longer if you have mild to moderate erectile dysfunction. Vardenafil. See more. 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 .