Viagra generally refers to sildenafil citrate tablets and its recommended dose is 50mg at a time, which can be reduced to 25mg or increased to 100mg depending on the individual. Sildenafil citrate tablets are mainly used to treat erectile dysfunction in men. It is routinely available in 25mg/tablet and 50mg/tablet with a recommended dose of 50mg to be taken about 1 hour before sexual intercourse. The dose can be increased to 100mg or decreased to 25mg depending on efficacy and personal tolerance. The recommended dose is 25mg for patients who are 65 years of age or older, have hepatic impairment, severe renal impairment, and are also taking a cytochrome P4503A4 inhibitor or erythromycin. Common adverse reactions after taking this product include abnormal vision, nasal congestion, nausea, dizziness, headache, flushing, and rash, and it is contraindicated in patients taking nitrate medications and in those who are allergic to this product. Please consult your physician before taking the drug, and should not blindly use the drug on your own.