Have you done a search on it for more info?
What size dose is he on?

It's not a long term drug, for some severe conditions it may be used for many many months especially if a person life depends on it.
But tapered down to go off it after long term use.

long term use = mood changes ( cranky, irritable), moon face, weight gain, bloating. may leach calcium out of bones & teeth...

and more-
http://www.drugs.com/methylprednisolone.html
http://www.rxlist.com/medrol-drug.htm