Viagra is absorbed rapidly after oral administration and takes effect in 10-40 minutes. Food can have an effect on absorption, and it needs to be taken on an empty stomach, and its effect lasts for about four hours. Viagra belongs to the type 5 phosphodiesterase inhibitor, which can increase the intracellular cyclic guanosine phosphate concentration, so that the blood flow of the arteries in the cavernous body of the penis increases and produces an erection, and it has a wide range of applications in men with erectile dysfunction and other diseases. However, the drug needs to be used in the presence of sexual stimulation in order to work as it should. This drug is a prescription drug and must be used appropriately under the supervision of a doctor. This drug has certain side effects that can cause gastrointestinal reactions such as nausea, vomiting, abdominal pain and diarrhea. In addition, cardiovascular side effects can also occur, such as the possibility of chest tightness, chest pain, dizziness and other adverse reactions. If you become unwell during the course of the medication, you need to seek immediate medical attention.