Continue to take tadalafil even if you feel well. What alternatives can I use for erectile dysfunction? In , Pfizer scientists discovered that sildenafil, which also inhibits the PDE5 enzyme, caused penile erection in males participating in a clinical study of a heart medicine. However, because sexual stimulation is required to initiate the local penile release of nitric oxide, tadalafil’s inhibition of PDE5 will have no effect without sexual stimulation. The decision of availability is completely up to the company marketing the product. Mechanism of action[ edit ] Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and the smooth muscle of the corpus cavernosum.Cialis is not covered by most Medicare and insurance plans, but manufacturer and pharmacy coupons can help offset the cost. Prices Medicare Drug Info Side Effects Images Cialis (tadalafil) is an expensive drug used to treat erection problems in men. Tadalafil – STADA T20 – 20 Milligramm. Tadalafil, sold under the brand name Cialis among others, is a medication used to treat erectile dysfunction, benign prostatic hyperplasia, and pulmonary arterial hypertension. [4] [5] [7] It is taken by mouth. [7] Onset is typically within half an hour and the duration is up to 36 hours. Roman sells the following versions of Cialis: Generic: available in tablets of 5, 10, and 20 milligrams (mg), starting from $11 Daily Generic: available in doses of and 5 mg at $8 Branded.