Online pharmacies can be broadly categorized as: Mail-order pharmacies are operated by pharmacy benefits managers PBMs on behalf of health insurers or providers. Online pharmacies also may not fill short-term prescriptions, such as those for antibiotics. Independent online pharmacies operate solely on the Internet, either domestically or internationally. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. Sildenafil Viagra. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED. You can take this medicine with or without food 30 minutes before sex, depending on the dose.Can you get Viagra without a prescription? You cannot legally get Viagra in the United States and most other countries without a prescription. The United Kingdom is one notable exception. Viagra alternatives range from medical options like Cialis and Levitra to natural methods like acupuncture and even therapy. We break them all down here. When you think of erectile dysfunction (ED. Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. This boosts blood flow and helps you get an erection from sexual activity. How oral medicines differ.