Tadalafil, sold under the brand name Cialis among others, is a medication used to treat erectile dysfunction, benign prostatic hyperplasia, and pulmonary arterial hypertension.

[8] Rare but serious side effects include a prolonged erection that can lead to damage to the penis, vision problems, and hearing loss.

[12] Tadalafil is FDA-approved for males as a therapy to treat and prevent symptoms of benign prostatic hyperplasia, such as urinary urgency, hesitancy, weak stream, dribbling, and incontinence.

[13] Tadalafil is approved in the United States, Canada, and Japan to improve exercise ability in people with pulmonary arterial hypertension.

[8] Also common are dizziness, peripheral edema, fatigue, and urinary or respiratory tract infection; both diarrhea and constipation have been reported.

[16] In May 2005, the US Food and Drug Administration (FDA) found that tadalafil (along with other PDE5 inhibitors) was associated with vision impairment related to NAION (non-arteritic anterior ischemic optic neuropathy).

[17] Most, but not all, of these patients, had underlying anatomic or vascular risk factors for the development of NAION, unrelated to PDE5 inhibitor use.

[8] The FDA concluded that they were not able to draw a cause and effect relationship, only an association; the label of all three PDE5 inhibitors was changed to alert clinicians to that fact.

[medical citation needed] cGMP relaxes smooth muscle and increases blood flow to the corpus cavernosum.

[medical citation needed] The inhibition of phosphodiesterase type 5 (PDE5) enhances erectile function by increasing the amount of cGMP.

Tadalafil was approved in 2009 in the United States for the treatment of pulmonary arterial hypertension[29] and is under regulatory review in other regions for this condition.

[30][31] In 1993, the Bothell, Washington, biotechnology company ICOS Corporation began studying compound IC351, a phosphodiesterase type 5 (PDE5) enzyme inhibitor.

In 1994, 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.

Soon, in 1994, ICOS received a patent for compound IC351 (structurally unlike sildenafil and vardenafil), and Phase 1 clinical trials began in 1995.

The FDA has also approved tadalafil for the treatment of both benign prostatic hyperplasia and erectile dysfunction where the two conditions co-exist.

In the United States, the FDA relaxed rules on prescription drug marketing in 1997, allowing advertisements targeted directly to consumers.

[36] Marketing for Cialis has taken advantage of its greater duration compared to its competitors in advertisements for the drug; Stuart Elliot of The New York Times opined: "The continuous presence of females in Cialis ads is a subtle signal that the drug makes it easier for them to set the pace with males, in contrast to the primarily male-driven imagery for Levitra and Viagra.

[38] In Australia, tadalafil is subsidized through the Repatriation Pharmaceutical Benefits Scheme (RPBS) for patients with a specific accepted war- or service-related disability.