Viagra generally refers to sildenafil citrate tablets, and the effects generally last for about 4 hours. Sildenafil citrate tablets are mainly used to treat erectile dysfunction. Sildenafil requires sexual stimulation and is usually taken 30 minutes to 4 hours before the start of sex, and the effect of the drug usually lasts for about 4 hours after taking it, but the exact duration varies depending on the individual’s physique. Common side effects of sildenafil citrate tablets include headache, facial flushing, stomach upset, muscle pain, nausea, dizziness, persistent erection, etc. Sildenafil is forbidden to be used in combination with nitrate drugs, and this drug is forbidden for women, those who are allergic to the product, children, and those whose recent cardiovascular status is not suitable for sexual life. If you have erectile dysfunction, you need to go to a regular hospital to find a professional doctor for a clear diagnosis before treatment, and the drug should be applied under the guidance of a doctor.