Our Lemonaid doctors or nurse practitioners can advise the right dose for you. Do I need a prescription for Tadalafil? Levitra vardenafil : This medication is taken one hour before sex and can last up to 24 hours. An erection results from an increase in blood flow to the penis. Medical consultations were also taken into consideration, as PDE5 inhibitors require a valid prescription from a licensed medical provider. The mechanism of action for ED pills is simple: They inhibit the PDE5 enzyme which regulates the signals responsible for the smooth muscle tissue.Tadalafil (Cialis) is available both as brand-name and generic tablets. Common side effects of this medication include headache and indigestion. Tadalafil . 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 . Best Low Cost: GoodRx Fastest Delivery: Blink Health: Sesame Sign Up Now Key Specs Cost: Consultation prices vary based on the prescriber; $5 generic .