They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Here are some key factors to consider when deciding: Pricing: Know how much your monthly supply will cost with shipping and tax. The body takes longer to absorb it after a high-fat meal or alcohol. The generic versions are just as effective and much less expensive. Make sure to get an estimate of when you can expect your prescription in the mail. Most online providers require a picture of a valid ID, a selfie showing your face, and a recent blood pressure reading taken with a home blood pressure monitor or by a medical provider.Medications Prescribed: Viagra, Cialis, Cialis Daily, Levitra, tadalafil, sildenafil, vardenafil. Generic offered: Yes. Why We Chose It. The simple combination of Rex MD’s online . Sildenafil (Viagra) may interact with certain medications or supplements. Always let your doctor and pharmacist know about any other medications or supplements (including . Viagra vs. over-the-counter products. Many over-the-counter (OTC) products may be advertised to help with ED. Examples of these products include: dehydroepiandrosterone .