The most common side effect.....erections, lol!
Ah mate all of the PDE5 inhibitors are quite safe providing your not taking NITRATES, often used for heart disease or ANGINA. However since their primary mechanism of action is vasodilation the following may occur in a dose related manner; headache, facial flushing, lowered BP, blurred vision. Start with a low dose initially about 25mg Viagra or 10mg of Cialis and enjoy. Incidentally I've prescribed many scripts for all of the PDE5 inhibitors and had one patient develop hypotension (yea he was taking Isordil...a nitrate) with the other having priapism (nine hour erection which responded quite nicely to a single corpora cavernosa epinephrine injection). He was 28 years old and took 400mg so "it would last all night", wish fulfilled, LMAO!