Could corticosteroids have any major side effects?

Depends on which one. There are categories of steroids. Also if oral or inhalers. Oral ones are generally avoided unless an auto immune issue. Inhalers are for respiratory illnesses and also different potency available. General side effects are voice changes on vocal cord. Thrush if not rinsing well and long term according to studies is possible over many years. One needs to worry about osteoporosis.