Sildenafil - Does it require a prescription?

Yes it requires a presciption.

BTW:

There is currently no therapeutically equivalent version of Viagra available in the United States.

Note: Fraudulent online pharmacies may attempt to sell an illegal generic version of Viagra. These medications may be counterfeit and potentially unsafe. If you purchase medications online, be sure you are buying from a reputable and valid online pharmacy. Ask your health care provider for advice if you are unsure about the online purchase of any medication.

https://www.drugs.com/availability/generic-viagra.html

Regards, masso.-