Sildenafil may cause side effects. If you are taking sildenafil for erectile dysfunction, you are unlikely to miss a dose since this medication is taken as needed, not on a regular dosing schedule. Take sildenafil at around the same times every day. Before starting, stopping, or changing any medications while taking sildenafil, please get the advice of your doctor or pharmacist. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine.You’ll typically take Viagra about 1 hour before sex. You can take the drug 30 minutes to 4 hours before you anticipate sexual activity. Based on how well you respond to this . Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online. 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 .