The active substance of Cialis, tadalafil, belongs to a group of medicines called 'phosphodiesterase type 5 (PDE5) inhibitors'. It works by blocking the phosphodiesterase enzyme, which normally breaks down a substance known as cyclic guanosine monophosphate (cGMP). During normal sexual stimulation,cGMP is produced in the penis, where it causes the muscle in the spongy tissue of the penis (the corpora cavernosa) to relax, allowing the flow of blood into the corpora, producing the erection.
By blocking the breakdown of cGMP, Cialis restores erectile function. However, sexual stimulation is still needed. By blocking the phosphodiesterase enzyme and preventing the breakdown of cGMP, Cialis also improves the blood flow to, and relaxes the muscles of, the prostate and bladder. This may reduce the problems with the flow of urine which are symptoms of benign prostatic hyperplasia.
