The danger comes from taking it with other drugs or getting it from someone without a medical license. You can take it in a small dose daily or in a larger dose as needed. Tadalafil Cialis. Online pharmacies don’t always hold up to scrutiny, either. You can take this medicine with or without food 30 minutes before sex, depending on the dose.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. There are no over-the-counter alternatives to Viagra. However, people may wish to try natural supplements that people can purchase without a prescription. Do you need a prescription for Viagra alternatives? Yes, if you are considering erectile dysfunction medications similar to Viagra — like Cialis, generic Viagra, and generic Cialis — it will.