I am allergic to solu-medrol is it safe to take decadron (dexamethasone)?

Depends: "allergy" to a medication is often used loosely to mean any adverse reaction so its difficult to give a definitive answer without a full history. Both drugs are potent corticosteroids given as injections. You should approach Decadron (dexamethasone) with caution if you have had a bad experience with solu-medrol. This is a situation where a frank discussion with your knowledgeable physician is a very good idea.

Same class: When one has an allergy to one member of a class of medications, it is usually not wise to take another in the class. Check with your prescribing provider about this 'allergy'. Often, the things that people call an allergy are really just unpleasant but expected effects from it's mechanism of action.