Cenforce 100 mg can be safe for some adults when prescribed appropriately, but it is not safe for everyone. It generally contains 100 mg of sildenafil citrate, the same active ingredient used in Viagra, and is used to treat erectile dysfunction (ED). The key issue is that 100 mg is the maximum usual recommended dose of sildenafil for ED, not the recommended starting dose for everyone. What you should know How it works: Improves blood flow to the penis during sexual stimulation. How quickly: Usually starts Cenforce 100 mg within 30–60 minutes. How long: Effects may last around 4–6 hours. Common side effects: Headache, facial flushing, indigestion, nasal congestion and dizziness. When should you avoid Cenforce 100 mg? If you take nitrate medicines for chest pain, including nitroglycerin or isosorbide. If you take riociguat for pulmonary hypertension. If you have serious heart or liver problems, very low blood pressure, or recently had a heart attack or stroke, until a doctor has assessed whether sildenafil is appropriate. If you already took another sildenafil product, such as Fildena or Malegra, that day. FDA Access Data +1 Seek emergency help for chest pain, fainting, sudden vision or hearing loss, or an erection lasting more than four hours.