Using alcohol or tobacco with certain medicines may also cause interactions to occur. If you will be taking this medicine for pulmonary arterial hypertension, your doctor will want to check your progress at regular visits. Men with untreated ED had relatively low baseline scores for all aspects of sexual function measured again using a 5-point scale in the IIEF. Especially tell your healthcare provider if you take any of the following: medicines called nitrates medicines called guanylate cyclase stimulators such as Adempas riociguat medicines called alpha-blockers, such as Hytrin terazosin HCl , Flomax tamsulosin HCl , Cardura doxazosin mesylate , Minipress prazosin HCl , Uroxatral alfuzosin HCl , Jalyn dutasteride and tamsulosin HCl , or Rapaflo silodosin. Children—Use is not recommended. If you experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. Both sildenafil and the metabolite have terminal half lives of about 4 hours.Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be. Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision. Low libido (reduced sex drive) can strike men at any age, but it becomes more common as a man gets older. It may be caused by: psychological factors, such as child abuse, depression, or relationship issues. physical factors, such as low testosterone or medication side effects (such as antidepressants, oral medications used to treat prostate Missing: canada.