What side effects can this medication cause? Concomitant administration of strong CYP3A4 inducers, such as rifampin, is expected to cause greater decreases in plasma levels of sildenafil. Both sildenafil and the metabolite have terminal half lives of about 4 hours. John’s wort. If you are taking sildenafil to treat erectile dysfunction, follow your doctor’s directions and the guidelines in this paragraph. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often.Getting a 3-month supply. You may be able to get a day supply of Viagra. If approved by your insurance company, getting a day supply of the drug could reduce your number of trips to the. VIAGRA is supplied as blue, film-coated, rounded-diamond-shaped tablets containing sildenafil citrate equivalent to 25 mg, 50 mg, or mg of sildenafil. Tablets are debossed with PFIZER on one side and VGR25, VGR50 or VGR on the other to indicate the dosage strengths. Close. If you have these symptoms, stop taking VIAGRA and contact a doctor right away. have or have had heart problems such as a heart attack, irregular heartbeat, angina, chest pain, narrowing of the aortic valve, or heart failure. have had heart surgery within the last 6 months. have pulmonary hypertension. have had a stroke.