Viagra generally refers to sildenafil citrate tablets and is taken up to once a night. Sildenafil citrate tablets are generally blue film-coated tablets that are used to treat erectile dysfunction in men and are taken up to once a day. Adverse reactions that may occur after taking Sildenafil Citrate Tablets include headache, dizziness, rash, visual abnormalities, and in more severe cases, neuralgia and asthma. In case of serious reactions, immediate response and medical attention is required. In addition, sildenafil citrate tablets are contraindicated in patients taking any dosage form of nitrate. And women, children, and people who are allergic to the drug should not take the drug. The drug needs to be used under the supervision of a doctor, do not buy it for self-medication.