Viagra generally refers to Sildenafil Citrate, and there are about 4 to 5 manufacturers producing this drug, but regardless of the manufacturer, its effect is the same, regardless of whether it is good or bad. Sildenafil citrate is a type 5 phosphodiesterase inhibitor commonly used in the clinic, which can effectively increase the hardness of the penis when a man gets an erection, and in the case of impotence patients, it can enhance the quality of their sex life. There are about 4 to 5 types of this drug on the market, but their efficacy is similar and there is no significant difference, all of them can be used safely. Sildenafil’s frequent side effects include back pain, muscle pain, dizziness, dyspepsia, flushing, headache, nausea, nasal congestion, and visual abnormalities, etc. It is forbidden for those who are allergic to this drug, and it should be noted that it cannot be combined with nitrate. Please purchase under the guidance of a physician and use the medication according to the doctor’s instructions, and should not be used blindly.