Sildenafil citrate 100 mg is a medication primarily used to treat erectile dysfunction (ED) in men. It belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. Sildenafil works by increasing blood flow to the penis during sexual stimulation, which helps men achieve and maintain an erection. It's important to note that sildenafil should be taken about 30 minutes to 1 hour before sexual activity and should not be taken more than once a day.