These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. Generic versions of sildenafil, vardenafil and tadalafil are available. Tadalafil is another licensed oral medication that treats ED, but it lasts for much longer — up to 36 hours Viagra only lasts around four hours. But, you should still see your doctor to discuss other health issues. Viagra, known as the blue pill, can be prescribed by doctors or clinicians in strengths of 25mg, 50mg, and mg. Sildenafil Viagra. But, keep in mind that ED might signal an underlying medical problem, like high blood pressure, heart disease, diabetes, low testosterone, or sleep apnea.A prescription from your GP may allow you to get Viagra (or unbranded Sildenafil) for a lower cost than over-the-counter Viagra Connect. It’s also advisable to speak to your . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . Health There’s a New Over-the-Counter ED Drug. Should You Be Taking It? Doctors say it could be a “game-changer.” By Erica Sweeney Published: Save Article .