Can you take magnesium oxide and allegra (fexofenadine) d together?

Yes: These 2 products can be taken together without any problems. Remember the "d" in Allegra (fexofenadine) d is usually pseudoephedrine, which can cause dry mouth, insomnia, rapid heart rate. Most people can get by with just plain allegra, (fexofenadine) if do need to use the "d" formulation, try to keep it to just a couple of days to reduce the congestion and then switch to just the Allegra (fexofenadine) for ongoing symptom control.