Both options require valid medical documentation, but some online services only require a health questionnaire to be filled out and reviewed for approval—meaning no face-to-face video interaction is needed. Box , Mission, KS If your pharmacy does not participate, you may be able to submit a request for a rebate in connection with this Savings Offer. If you prefer, you may contact the U. Erectile dysfunction medications require a prescription from a licensed provider. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. 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.Common Brand(S): Viagra Generic Name(S): sildenafil. Uses; Side Effects; Precautions; Interactions; Overdose; nor should it be construed to indicate that use of a particular drug is safe. Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 hour. In addition to Viagra, REX MD also offers brand-name Cialis and generic Cialis (tadalafil). Both Viagra and sildenafil are available in mg, mg, and mg doses.