Viagra is mainly used to improve male sexual function and to treat erectile dysfunction in men, and the onset of action is usually relatively fast. Usually, a certain therapeutic effect can be exerted half an hour after taking the drug, and the best therapeutic effect can be achieved one hour after taking the drug. Therefore, it is recommended that patients take it as needed about one hour before sexual activity, and the effect can be maintained for four hours. However, it usually has a better therapeutic effect in the first two hours, and in addition it needs to be taken under conditions of sexual stimulation to be able to exert its therapeutic effect. Therefore, it is important to have sexual stimulation at the time of use, otherwise it will be difficult to exert the therapeutic effect. In conclusion, Viagra can improve the erectile dysfunction of patients, but when using it, you should pay attention to the precautions and methods of administration.