Viagra, scientifically known as sildenafil, is a drug used to treat male sexual dysfunction and can improve the quality of a man’s sex life. It is more commonly used for people who have erectile dysfunction. Viagra causes the blood vessels of the penis to dilate through its special chemically active action, causing the arterial sinuses of the penile corpus cavernosum to fill with blood, and this action can help the penis to become erect. Since the drug takes time to metabolize, it can also maintain an erection for a period of time and enhance the hardness of the cavernous body after erection, which facilitates the completion of sexual life. Some studies surface that the maintenance time of this drug can generally reach 2-3 hours, and in special cases, can maintain the effect for up to 5 hours. This drug is relatively safe in most cases. However, there can be some side effects of the drug. The most common side effects include: headache, nasal congestion, impaired vision, photophobia, or sensitivity to light, indigestion, and in rare cases, Viagra use can lead to non-arteritic anterior ischemic optic neuropathy or optic nerve damage. These conditions are very unlikely to occur, but there are side effects. Severe cases of sudden death have occurred. Viagra is a drug used to treat male sexual deficiencies, but most people do not use it very regularly. To minimize the appearance of side effects, it is best to use it under the guidance of a professional doctor.