Precautions It is important that you tell all of your doctors that you take sildenafil. Use protective measures and ask your doctor if you have any questions about this. However, if you take sildenafil with a high-fat meal, it will take longer for the medication to start to work. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine. 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.Sildenafil is used to treat erectile dysfunction (ED) and to reduce blood pressure in pulmonary arterial hypertension (PAH). It is taken when needed for ED and daily for PAH. A headache, stomach upsets, and flushing are the main side effects, and it should not be taken within 24 hours of a nitrate. 5. Tips. Prices at Rite Aid Pharmacy for Popular Prescriptions. Drug Name. Lowest GoodRx Price. tadalafil (Cialis) (Generic Cialis) 30 tablets 5mg. $ with free Coupon. Get Free . Estimated Retail Price Lowest GoodRx Price Savings with GoodRx; sildenafil (Generic Revatio, Viagra) 30 tablets mg. $1, $ with free Coupon. 98%. Get Free .