Viagra generally refers to sildenafil citrate, the phenomenon of swelling in the lower body after a man takes it is mainly considered to be related to drug effects, adverse reactions and other factors. 1. drug effects: sildenafil citrate is a drug used to treat erectile dysfunction in men, after the application, it will promote penile erection, and prolonged erection will lead to prolonged penile congestion, which can lead to penile swelling, pain and other symptoms. 2. Adverse reactions: the symptoms of penile swelling, should also be alert to the possibility of adverse drug reactions. And there are reports that some patients have abnormal erections for more than 4 hours after taking the drug, which can also lead to penile swelling and pain, and must seek medical attention in a timely manner. 3. Other factors: most patients will have sex after taking the drug, if the action is too violent, resulting in penile injury, can also trigger penile swelling. The above symptoms should be taken seriously, consult a doctor as soon as possible to confirm the diagnosis, and follow the doctor’s instructions for treatment.