If you take too much Taking too much sildenafil can cause unpleasant side effects. Do not take other medicines unless they have been discussed with your doctor. Proper Use Use sildenafil exactly as directed by your doctor. It is not recommended for use in Australia. What side effects can this medication cause? Causes of erectile dysfunction The exact cause of ED can be hard to pinpoint because there are many conditions to consider.Last updated on Uses. Warnings. Before taking. Dosage. Side effects. Interactions. FAQ. What is Viagra? Viagra relaxes muscles found in the walls of blood . There is also a generic version of Viagra available, under the name sildenafil, in 25mg, 50mg, and mg strengths. 3. Downsides. If you are between the ages of 18 and 60, .  · It is important to tell your doctor about any heart problems you have now or may have had in the past. This medicine can cause serious side effects in patients with heart problems. If you experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately.