Talk to your doctor if you take too much sildenafil and you’re worried about any of these side effects: headaches. Do not take more or less of it or take it more often than prescribed by your doctor. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. Be sure to let your doctor and pharmacist know that you are taking these medications before you start taking sildenafil. Before starting, stopping, or changing any medications while taking sildenafil, please get the advice of your doctor or pharmacist. 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 also available in generic form. Viagra is classified as a Do you really need to walk 10, steps to see health benefits? Viagra is a prescription drug used to treat erectile. There is also a generic version of Viagra available, under the name sildenafil, in 25mg, 50mg, and mg strengths. 3. Downsides The dosage may need to be reduced in people with kidney or liver disease. (Viagra) for ED, do not take it more than once a day. Take an hour before sexual stimulation (range 30 minutes to 4 hours). Sildenafil tablets for erectile dysfunction come in different strengths ranging from 25mg to mg. The usual dose is 50mg, when you need it. Do not take it more than once a day. The dose can be increased to mg or decreased to 25mg depending on its effect. Take sildenafil up to 4 hours before you want to have sex.