The drug ViagraTM is the name given to sildenafil citrate, because the drug is administered as the citrate . Sildenafil citrate is a white crystalline powder which is formulated in a blue, rounded-diamond-shaped, film-coated tablet. it is available in tablets of different amounts of sildenafil: 25, 50 and 100 mg of sildenafil for oral administration.

The tablets contain the following inactive ingredients (in addition to sildenafil) : microcrystalline cellulose, anhydrous dibasic calcium phosphate, croscarmellose sodium, magnesium stearate, hydroxypropyl methylcellulose, titanium dioxide, lactose, triacetin and FD and C Blue#2 aluminium lake.

The clinical studies on Viagra lasted 5 years and 3,000 patients participated in the tests. Sildenafil citrate was assessed for its effect on the ability of men with erectile dysfunction to engage in sexual activity and to achieve and maintain an erection sufficient for sexual activity. The effectiveness of the drug was assessed primarily through a questionnaire, the International Index of Erectile Function, IIEF. This questionnaire was created for the study of sildenafil citrate but is now used in many other studies. The questions related to (1)the ability to achieve erections sufficient for sexual intercourse and (2)the maintenance of erections after penetration. Patients also kept a daily diary.

Several side effects of sildenafil citrate were reported, during the trials as well as after marketing had started. The most commonly encountered are headaches, facial flushing, nasal congestion, urinary tract infection, diarrhea, upset stomach and muscle aches in the pelvic area.
Of the most talked about are serious cardiovascular events, including sudden cardiac death which have frequently been talked of in the media. Not all of the patients who suffered these effects had preexisting cardiovascular risk factors, although this was true for most. Many of these events were reported to have happened during or after sexual activity with the use of Viagra. The reason for these problems comes from the fact that organic nitrate drugs (which are present in nitrate vasodilator drugs taken for hypertension/heart disease) act by acting a Nitric Oxide donors. These increase the levels of cGMP at the same time as Viagra inhibits its degradation. This creates an extremely large increase in cGMP levels which can end in a catastrophic drop in systemic blood pressure. This can lead to a heart attack. Another well talked of side effect is abnormalities related to colour vision (impairement of colour discrimination blue/green). This was reported by about 3% of patients in clinical trials.