Yes, like all medications, Fildena can have negative effects, though not everyone experiences them. Fildena contains sildenafil citrate, the same active ingredient found in Viagra, and is mainly used to treat erectile dysfunction (ED). While it is effective for many men, it can cause side effects ranging from mild to severe, depending on the dosage, overall health, and possible drug interactions. The most common side effects of Fildena are usually mild and temporary. These include headaches, facial flushing, nasal congestion, dizziness, and indigestion.