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. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. Contact your medical provider if you experience any side effects during treatment. It’s available in 10 mg and 20 mg tablets. Privacy: Confirm that your personal data and payment details are confidential.It also allows you to get an online prescription (e-prescription) quickly, without having to go visit your provider. This is true whether you have mental health concerns or acne or you need birth control or refills for a chronic condition. 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. According to price-comparison site , generic Revatio will cost you as little as $ per pill, depending on where you fill your prescription. That’s compared with more than $50 per.