Do not keep outdated medicine or medicine no longer needed. This medicine can cause serious side effects in patients with heart problems. Precautions It is important that you tell all of your doctors that you take sildenafil. It is important to tell your doctor about any heart problems you have now or may have had in the past. What alternatives can I use for erectile dysfunction? It affects the way the medicine works.AdTrust Our Unbiased Reviews and Improve Your Sexual Health in Confidence! Say Goodbye to Performance Anxiety and Hello to Improved Sexual Stamina!Honest & Unbiased Reviews · Over 20 Years Online · Over Products Tested. Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online. Cialis lasts up to 36 hours in the body, while Viagra lasts 4–6 hours in the body. Both are taken 30 minutes before sex. Cialis can cause limb pain, while Viagra can cause vision change, rash.