Viagra, generally referred to as sildenafil, is usually available at drugstores for about $20 to $100 depending on the region as well as the brand. Sildenafil is a PDE5 inhibitor drug used to treat erectile dysfunction in men. The price is not fixed due to various factors such as manufacturer, sales channels, specifications, packaging, imported or domestic and so on. Currently, its selling price for a box ranges from $20 to $100. The specific price is subject to local pharmacies and medical institutions. However, the drug belongs to the category of prescription drugs and must be prescribed by a doctor before purchase and use. The drug is usually taken one hour before sexual intercourse. Some patients may experience adverse reactions after taking it, such as dizziness, headache, flushing, and blurred vision. Sildenafil should never be taken blindly. The main common adverse reactions of this drug are headache, flushing, dizziness, nasal congestion, indigestion, and visual abnormalities. The drug is forbidden to be combined with nitrate drugs, and it is contraindicated for women, people who are allergic to the product, children, and people whose recent cardiovascular state makes them unfit for sexual intercourse. Patients taking sildenafil citrate tablets should consult a doctor before using the drug and take it under his or her guidance, do not take it blindly on your own.