Viagra is scientifically called sildenafil citrate and usually lasts for about 0.5-4 hours time. Exactly how long needs to be based on the patient’s ability to absorb the medication. Sildenafil Citrate is used to improve male sexual function and treat erectile dysfunction. Generally take sildenafil citrate tablets can adhere to 0.5-4 hours, for the degree of absorption of the drug effect is relatively poor, adhere to the time of about 30 minutes, the specific time needs to be based on the patient’s ability to absorb the drug to judge. Sildenafil citrate side effects such as shock, vomiting, chills and accidental injury can occur in some patients after taking it. The drug is forbidden to be used in combination with nitrate drugs, and it is contraindicated for women, people who are allergic to the product, children, and people whose recent cardiovascular status makes them unfit for sexual intercourse. Sildenafil citrate can not be taken orally, patients are advised to take it under the guidance of a specialized doctor. Adverse reactions during the use of the drug, it is recommended to stop the drug in time and go to the hospital.