Viagra is the trade name and generic name for sildenafil citrate tablets, which usually do not work without sexual stimulation after taking sildenafil citrate tablets. Sildenafil citrate tablets are phosphodiesterase type 5 inhibitors used to treat erectile dysfunction. The drug is an on-demand medication that needs to be taken 30 minutes to an hour before sex, and after taking it, it must be sexually stimulated for it to work; without sexual stimulation, it will not work to improve erectile function. It is also not recommended to drink alcohol while taking the drug, and cannot be taken at the same time with nitrate drugs. The common adverse reactions of Sildenafil Citrate Tablets mainly include headache, flushing, dizziness, nasal congestion, indigestion, visual abnormalities, etc. It is recommended to use the medication under doctor’s supervision.