Cialis is the oral prescription drug of the generic compound tadalafil. The compound, developed by the biotechnology company ICOS, is mainly for the treatment of erectile dysfunction (ED) or impotence in men. Tadafadil was eventually developed and marketed by its brand name Cialis by Lilly ICOS, the joint venture of ICOS and Eli Lilly and Company.
 
On August 19, 2003, it was approved for sale in the United States by the Food and Drug Administration. Its development is closely linked with Viagra, the precursor of this class of drugs which treat ED. In fact, in 2000, Pfizer and Lily ICOS had been engaged in a legal battle over the patent of sildefinil, the active ingredient of Viagra. Eventually, Pfizer lost a part of its patent, relating to the use of phosphodiesterase 5 (PDE 5) inhibitors in the treatment of impotence (the way in which sildenafil works).

Cialis mode of action

Low levels of the hormone testosterone is one of the many causes of ED. Bodybuilders who are coming off their steroid cycle can experience depressed testosterone level, thus drugs like Cialis can be helpful as part of PCT stack. Cialis can be an assurance when you need to rise to the occasion and you’re still waiting for your natural hormone production to kickstart.
Cialis, also known as IC351, is a phosphodiesterase type 5 (PDE5) enzyme inhibitor. PDE5 is responsible for breaking down cyclic guanosine monophosphate (cGMP). cGMP causes the smooth muscle to relax for an ideal inflow of blood to the penis leading to an erection. Cialis inhibits PDE5 resulting to an increased amount of cGMP, which eventually enhances erectile function. This is basically the same mechanism of action of Viagra and other impotence drugs – they inhibit the enzyme PDE5. However, Cialis has pharmacologic advantage over any other drug of its class - its longer half-life. Cialis has a half life of 17.50 hours while Viagra and Levitra (another popular ED drug) have half-lives of only 4.0–5.0 hours.

Cialis use has significantly longer duration of action, thus its monicker of "The Weekend Pill". The longer half-life of this drug is why it is being eyed for the treatment of pulmonary arterial hypertension (PAH). The drug Revatio (sildefanil) is used to treat this illness; however, PAH patients have to take Revatio for up to three times daily.

Dosage

Cialis is recommended as a once-daily medication. The dosage advice is to start at 10mg, which can be increased (20mg) or lowered (5mg) depending on the user’s tolerance and response to the drug.  

Side effects

The most common side effects of Cialis are headache, upset stomach, backache and muscle ache.  On rare instances, sudden loss of hearing, dizziness and vision impairment have also been known to occur with Cialis use.