Sildenafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. Refills: See if you can set up automatic refills or order as needed. We considered cost, medications available, and whether generic versions were offered to help reduce costs. A phone or video consultation is sometimes required for legal purposes. If you buy sildenafil for erectile dysfunction, it can also be known by the brand names Viagra, Aronix, Liberize and Nipatra. The specific process for getting ED pills online depends on your chosen provider.Can I buy generic Viagra without a prescription? No. In most countries, including the United States, Viagra is not available without a prescription.  · Take sildenafil exactly as it was prescribed for you. Follow all directions on your prescription label and read all medication guides or instruction sheets. Revatio is usually taken three times each day, about 4 to 6 hours apart. Viagra is usually taken only when needed, 30 minutes to 1 hour before sexual activity. This medicine is available on prescription and you can also buy it from most pharmacies. It comes as standard tablets, chewable tablets, and as a liquid that you swallow. Key facts. It usually takes 30 to 60 minutes for sildenafil to work for erectile dysfunction. You can take it up to 4 hours before you want to have sex.