You have to declare your using them to your AME if you don't its illegal. And any self medicate steriods I would suspect would result in getting grounded.
Prescribed steriods from the folk I know who have taken them again its up to the AME if you can continue to fly.
I know guys who have had a jab go flying the next day with approval. Others that had 3 weeks to stabalise then were allowed to fly. And others that were grounded.
Steriods are pretty nasty drugs to be honest, the folk that I know who unfortuately have to take them long term have some pretty nasty side effects and seem to play a huge game of fiddling with the dosages constantly. And when they get the dosage wrong things get pretty nasty pretty quickly.