If Cenforce 25 mg contains sildenafil 25 mg, someone who has previously had an allergic reaction to sildenafil or any ingredient in the tablet should avoid it. The reaction can include rash, hives (urticaria), swelling, or—rarely—a serious anaphylactic reaction. You may be at higher Cenforce 25 mg  if you have: Previously developed an allergy to Viagra or another sildenafil product. Had an unexplained allergic reaction after taking a similar ED medicine. Known allergies to one of the tablet's inactive ingredients. Get emergency help if after taking it you develop swelling of the lips/face/throat, difficulty breathing, severe dizziness, or fainting. If you tell me what allergy you have or what happened when you took Cenforce, I can help determine whether it sounds like an allergic reaction or a more typical side effect.