This boosts blood flow and helps you get an erection from sexual activity. Oral medicines for ED usually work well and cause few side effects. They are all approved for treatment of erectile dysfunction. There are possible drug interactions with other prescription drugs for antibiotics, antifungals, antidepressants, high blood pressure, and some other drugs for medical conditions. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects. Both start from about half an hour after you take them, which means no long delays before you get down to business.Tadalafil is in a class of drugs called phosphodiesterase-5 (PDE5) inhibitors and is available in a generic form often called generic Cialis. Tadalafil has been on the . By Mayo Clinic Staff Medicines that you take by mouth are called oral medicines. They’re often the first line of treatment for trouble getting or keeping an . Tadalafil (Cialis) is taken by mouth either as needed before sexual activity or once daily for erectile dysfunction (ED).It’s also taken once daily to treat symptoms from .