BigFun is a brand name for a medication primarily used to treat erectile dysfunction (ED) in men. The active ingredient in BigFun tablets is sildenafil citrate, which is also the active ingredient in Viagra, a well-known medication for ED. Sildenafil citrate works by increasing blood flow to the penis during sexual stimulation, enabling men to achieve and maintain an erection. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors.