What is cialis?

The information at Pharmafund.Net is not a substitute for medical advice. ALWAYS consult your doctor or pharmacist.


Tadalafil, known under the brand name Cialis for the treatment of erectile dysfunction and Adcirca for pulmonary arterial hypertension, is a PDE5 inhibitor. Its main competitors are sildenafil citrate (Viagra) and vardenafil (Levitra).

Tadalafil’s chemical formula is C22H19N3O4.

Cialis became nicknamed “the weekend pill” because its effects last 36 hours. Viagra and Levitra are effective for up to 8 hours.

A PDE5 (phosphodiesterase type 5) inhibitor is a medication used to block the degradative action of cyclic GMP (cGMP) in the smooth muscle cells that line the blood vessels that supply the corpus cavernosa (two tubes that run the length of the penis). PDE5 is also present in the smooth muscle of the walls of the arteries within the lungs – hence, it has also been explored for pulmonary hypertension treatment.

Tadalafil was initially researched and developed by the ICOS Corporation, and then later on by Lilly ICOS LLC.

Cialis tablets appear in yellow, film-coated and almond shaped tablets in 5, 10 and 20 mg doses. Cialis for daily use is available as 2.5 mg and 5 mg tablets. Patients with pulmonary arterial hypertension take 2 x 20mg tablets once a day.

Cipla, a pharmaceutical company in India, manufactures and sells tadalafil under the brand name Tadacip.

Cialis was approved by the US FDA (Food and Drug Administration) on 21st November, 2003 for the treatment of erectile dysfunction. In May 2009 tadalafil was approved by the FDA for the treatment of pulmonary arterial hypertension.

Patients with erectile dysfunction take Cialis as needed. It should not be taken more frequently than once every 24 hours. For the medication to work, the man needs to be sexually aroused – it does not provide an instant erection without sexual stimulation.

How does an erection occur? What does Cialis do?

Penile erection occurs when the penis fills with blood. This happens because the blood vessels that bring blood flow to the penis dilate, thus increasing the blood supply. Simultaneously, the blood vessels that remove blood from the penis contract, so that blood accumulates (resulting in an erection).

When a man is sexually stimulated nitric oxide is released into the penis. Nitric oxide makes guanylate cyclase (an enzyme) produce cGMP (cyclic guanosine monophosphate). cGMP controls the dilation and contraction of the blood vessels that carry blood to and from the penis – when those supplying the penis with blood are dilated, and the others that remove blood from the penis are contracted, an erection occurs.

Another enzyme, phosphodiesterase-5 destroys cGMP. When this occurs the blood vessels return to their normal size and the erection ends. Tadalafil stops phosphodiesterase-5 from destroying cGMP, i.e. it prolongs the duration of cGMP, which results in a prolonged and better erection.

Important information about Cialis

Taking Cialis with a nitrate medication can cause a serious and sudden drop in blood pressure (hypotension). Do not take tadalafil if you are on a nitrate drug prescription for heart problems or chest pain.

If during sexual activity you feel dizzy or nauseated, or if you experience numbness, tingling or pain in your jaw, arms, neck or chest, stop and call your doctor immediately. This could be one of Cialis’ serious side effects (rare).

If after taking Cialis your erection last more than four hours, or if it is painful, get medical help. Priapism (prolonged erection) can damage the penis.

Cialis can sometimes (rare) undermine the blood flow to the optic nerve of the eye, causing sudden loss of vision. It is more likely to occur if the patient has hypertension, diabetes, high cholesterol, has certain pre-existing eye problems, or heart disease. Experts are not sure whether it is the tadalafil or something else that causes the vision loss.

People with the following conditions should not take Cialis (unless their doctor says it is OK):

  • People with heart rhythm problems
  • Patients with a recent history of congestive heart failure or stroke (within last list months)
  • Those with sickle cell anemia, multiple myeloma, leukemia or another blood cell disorder
  • Patients with hemophilia
  • People with liver or kidney disease
  • Individuals with a stomach ulcer
  • Patients with retinitis pigmentosa
  • People with Peyronie’s disease, or some other structural deformity of the penis
  • Those with heart disease
  • People who have been advised not to have sexual intercourse for health reasons
  • Individuals with Angina, or blood pressure problems (high or low)