Fildena 50 mg, which contains sildenafil citrate, can cause headaches due to its mechanism of action as a phosphodiesterase type 5 (PDE5) inhibitor. Sildenafil increases blood flow by relaxing the blood vessels, including those in the brain. This vasodilation can lead to a temporary drop in blood pressure and an increase in blood flow, which may trigger headaches in some individuals. Additionally, the widening of cerebral blood vessels is a known cause of headaches. Dehydration, increased heart rate, and sensitivity to the drug can also contribute. These headaches are typically mild to moderate and often resolve as the drug wears off.