The duration of action of one tablet of Viagra is usually 4 hours, but studies have shown that its effect is weaker after 2 hours, but there are individual differences and each person’s reaction to Viagra may be different. The generic name of Viagra is sildenafil citrate tablets, which are used to improve erectile dysfunction in men. It is generally recommended to take it one hour before sex because the peak blood concentration time is 0.5-2 hours after taking Viagra, with most patients reaching the peak in one hour. If there are other reasons for not being able to take it on time, there are studies that show that it can be taken between 0.5-4 hours of sexual intercourse. In addition, the drug must be taken under conditions of sexual stimulation to make it effective. The specific usage of Viagra should be taken in accordance with medical advice and the recommendations of the drug manual. It is not recommended to rely on drugs for a long time.