What are the symptoms of a dextromethorphan allergy in general so I can compare?

Rash, breathing. Dextromethorphan can cause direct histamine release, resulting in a rash, nausea, dizziness, and breathing difficulty. At high doses hallucination are possible.

Related Questions

Symptoms of a dextromethorphan allergy?

Not likely. Delsym (dextromethorphan) can cause adverse reactions in some people, such as nausea, dizziness, fatigue or abdominal pain. These are infrequent in nature. I am not aware of any cases of dextramethorphan allergy.