The shot was likely Depo Medrol which is a long acting (like about 3-4 weeks long) cortisone (steroid) which helps the body stop overreacting to allergens.
Most vets don't like to give cortisone if not truely necessary because repeated or consistant use messes up the body's natural ability to make cortisol on it's own. It also decreases the pet's immune system from fighting off infections. In some pets it causes an increase in thirst and hunger, in some cases resulting in accidents in the house. Despite it's downsides, Cortisones do have their uses and it helps a great many pets from suffering from certain problems.
If you're into in depth reading on Depo here's a link. http://www.drugs.com/vet/depo-medrol.html
Bookmarks