There is no such thing as which one is harder, tadalafil or vardenafil, both drugs belong to the same class of drugs, both belong to the selective type 5 phosphodiesterase inhibitors. Tadalafil and vardenafil are mainly used to treat penile erectile dysfunction. After taking them, sexual stimulation leads to the release of carbon monoxide, which, by selectively inhibiting phosphodiesterase type 5, leads to an increase in cyclic guanosine phosphate levels in the corpus cavernosum, resulting in relaxation of the smooth muscles and blood flow into the penile tissues thus producing an erection, which does not occur without sexual stimulation. The drug has adverse effects such as abdominal pain, nausea, vomiting, headache, tachycardia and facial flushing. The drug is prohibited for those who are allergic to the components; it is prohibited while taking nitrate drugs. With erectile dysfunction, it is recommended to first go to the hospital for examination and treatment as prescribed by the doctor, and the drug should be applied under medical supervision.