Viagra generally refers to sildenafil, which, as of now, is only available as an oral tablet, not as a topically applied preparation, and no studies have shown that sildenafil can be absorbed through the skin and mucous membranes. Sildenafil is a selective inhibitor of phosphodiesterase V, which enhances vasodilation caused by the release of NO during sexual stimulation, thus enhancing the physiological response to penile erection. Clinically, sildenafil is primarily used to treat erectile dysfunction (commonly known as impotence) in men. It is currently only available as an oral tablet. As an oral drug, the safety of sildenafil is good, common adverse reactions are mainly cardiovascular system reactions, such as the occurrence of myocardial infarction, heart failure, arrhythmia, hypotension, transient local ischemic shock, etc., but also dyspepsia, diarrhea, nasal congestion, urinary tract infections, headache and other reactions. It should be noted that the use of sildenafil is prohibited in patients who are allergic to sildenafil or who are using nitroglycerin, sodium nitroprusside or other drugs containing organic nitrates. It should be used with caution in patients with cardiovascular disease and patients with anatomical deformities of the penis. The specific use of sildenafil needs to be carried out under the guidance of a professional physician, the treatment should not choose to apply on their own to avoid adverse reactions.