The usual duration of action of 20 mg of tadalafil is between 24 and 36 hours. That implies you can take tadalafil and perhaps get an erection anytime between 30 minutes and 36 hours later. To be clear, Generic Cialis 20mg only works if you're feeling sexually stimulated.Tadalafil is an inhibitor of phosphodiesterase-5 (PDE5), an enzyme responsible for reducing erectile dysfunction. Blood vessel relaxation is aided by nitric oxide, which is degraded by the enzyme PDE5. Since tadalafil inhibits Phosphodiesterase type 5, more nitric oxide is retained in the body, which may enhance blood flow to the penis and result in an erection.Tadalafil absorption can be slowed by eating a large meal before taking the drug, which may reduce the drug's effectiveness. Talk to your doctor about the longevity of tadalafil use if you're concerned. They can recommend an appropriate dosage and offer tips for extending the effects.