Use the oral syringe provided with your medication to measure and take your dose. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. Tell your doctor or pharmacist if you are taking nitrates medications for chest pain such as isosorbide dinitrate Isordil , isosorbide mononitrate Monoket , and nitroglycerin Nitromist, Nitro-Dur, Nitrostat. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly.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 drug that’s used in adult males* . Side Effects. Dizziness, headache, flushing, or stomach upset may occur. Vision changes such as increased sensitivity to light, blurred vision, or trouble telling blue and green . Ways to save on Viagra. Save at least $5 per month on your prescription. Save at least $5 per month on your prescription. Call to get more information on how they can financially .