Viagra generally refers to sildenafil citrate tablets, which are used for the treatment of male sexual dysfunction. After taking it, you may experience an erection of the penis in response to sexual stimulation, and you may also experience side effects such as dizziness and headache, facial flushing, and nausea. Under normal circumstances after taking the medicine, the penis will become erect under stimulation, which is a normal reaction after taking sildenafil tablets. Some patients may feel uncomfortable after using the drug, often headache and dizziness, facial flushing, dyspepsia and other adverse reactions, after stopping the drug, the symptoms can disappear on their own. The drug can not be combined with nitrate drugs, which will cause a sharp drop in blood pressure. It should also be noted that with heart disease, kidney disease, etc. to avoid serious consequences, try not to take the drug. Sildenafil citrate tablets are prescription drugs and should be taken in accordance with medical advice, paying attention to dosage and usage. If you experience any discomfort after taking the medicine, you should go to the hospital for treatment in time.