Viagra, also known as sildenafil citrate tablets, is recommended to be taken 1 hour before sexual intercourse. There is usually a more pronounced response within 1 hour of taking the drug, which can have a better therapeutic effect. Viagra is mainly used for the treatment of erectile dysfunction in men, because after the drug is taken orally, the blood concentration in the body usually peaks at 0.5-2 hours, and the average time to reach the peak blood concentration is 1 hour. Therefore, taking it 1 hour before sex will have a better therapeutic effect. The duration of action of Viagra is about 4 hours, and it may have some effect within 4 hours, but research shows that the effect is usually more obvious in the first 2 hours and weaker in the last 2 hours. The effect of Viagra must be under the condition of sexual stimulation to be able to play the therapeutic effect, if there is no sexual stimulation is difficult to play the effect.