Sildenafil citrate 100 mg is a medication commonly used to treat erectile dysfunction (ED) in men. It works by inhibiting the phosphodiesterase-5 (PDE-5) enzyme, which increases blood flow to the penile tissues during sexual stimulation and helps achieve and maintain a firm erection. The 100 mg strength is generally considered a higher dose and is prescribed when lower doses are not sufficiently effective. It should be taken about 30–60 minutes before sexual activity and only once within a 24-hour period. Common side effects may include headache, flushing, nasal congestion, dizziness, and indigestion. It should be used under medical guidance, especially for individuals with heart conditions or those taking nitrate medications.