Allergic reactions to medications like Penegra 100 mg (which contains sildenafil citrate) are rare but possible. If you have a known allergy to sildenafil or any other ingredients in Penegra, you should not take it.

Symptoms of an allergic reaction to Penegra or sildenafil can vary but may include:

Rash or hives
Itching or swelling, especially of the face, tongue, or throat
Difficulty breathing or swallowing
Dizziness or lightheadedness
Nausea or vomiting
If you experience any signs of an allergic reaction after taking Penegra 100 mg, seek medical attention immediately. Allergic reactions can be serious and require prompt treatment.

It's also important to be aware of potential side effects of Penegra 100 mg that are not necessarily indicative of an allergic reaction but should be reported to your healthcare provider if they occur. These side effects may include headache, flushing, stuffy or runny nose, indigestion, dizziness, or changes in vision or hearing.