Side effects associated with Sildenafil Citrate.

There are a variety of side effects related to the use of Sildenafil. Perhaps the most notorious is sudden heart attacks)myocardial infarctions) during sexual activity, along with the blue hue associated with vision when using the drug. This page takes a look at the major side effects and their biological origins.(See Biological Mechanism)

Cardiac problems such as myocardial infarction, ventricual arrythmia, though it is impossible to distinguish whether the use of Viagra or sexual activity is the actual cause. Other side effects are:


2-Nervous seizures


4-Nasal congestion

5-Urinary tract infection

6-Abnormal vision- Blue tinge also increased sensitivity to light and blurring. The enzyme PDE6 is involved in phototransduction in the retina. Thus it is not surprising that Viagra; a PDE inhibitor affects this system.




10-Priapism: painful erections lasting longer than 6 hours)


Effects of other drugs on Viagra:


Cytochrome p450 related effects:

Cimetidine(800mg), a non-specific CYP inhibitor caused an increase of 56% of the blood concentration of sildenafil, if taken with Viagra. Erythromycin, a specific CYP3A4 inhibitor caused an increase of 184%

Viagra has been shown to weekly inhibit a variety of isoforms of the cytochrome p450 - 1A2, 2C9,2C19,2D6 2E1 as well as 3A4. It is unlikely that Viagra will effect the removal of substrates from these isoforms due to low blood plasma concentrations.

Despite the use of CY2C9 for the removal of sildenafil, tolbutamide(250mg) and Warfarin*40mg), both of which are metabolised by the same isoform had no effect on Sildenafil removal.

As viagra is a new drug on the market these side effects reflect those known at this time (Jan 1999), as a result of preliminary reports. Almost certainly, more will come to light.

Click for project information:{short description of image}