Viagra generally refers to sildenafil, a reasonable dose of this drug is recommended to be taken 2 times in a week by healthy adult males with no contraindications to the drug, provided that the diagnosis of erectile dysfunction is clear. Sildenafil can be used to treat penile erectile dysfunction in men. For healthy adult males with no contraindications, no underlying medical conditions, and a reasonable dosage of the drug (single <100 mg), it is recommended to take the drug 2 times a week. It can also be taken on demand, 30 minutes to 1 hour before sexual intercourse. The drug is contraindicated in allergic individuals, and its concomitant use with nitrates (such as nitroglycerin, etc.) is strictly prohibited. The drug is also contraindicated in women, children, people whose recent cardiovascular state does not allow them to have sex. Adverse reactions to the drug mainly include flushing, indigestion, nasal congestion, headache and so on. Specific use should strictly follow the instructions of the clinician in order to avoid the occurrence of adverse events.