In areas of high moisture such as walls in a shower for long term durability it is not advised to install tile over drywall even if the drywall is type mr moisture resistant.
Shower wall tile and joint with dry wall.
If your tiles are in mortar break open a.
Furthermore blueboard is not difficult to install.
It will be fine to tile over drywall in low moisture areas such as tiling around a fireplace.
This joint needs to be flush and smooth in order for the tile or other wall covering to be installed correctly and to create a professional finished appearance.
If the tiles are mounted on drywall the moisture will eventually turn the drywall to a messy mush.
The bottom line is that drywall and this includes moisture resistant drywall should never be used behind tile in wet areas showers and tub shower combinations.
Blueboard is a type of drywall that is frequently used for a tile wall in a shower.
If you have a larger area break the tiles with a hammer and chisel or sledgehammer to get them off the drywall then unscrew and pull down the old panels.
In areas that are exposed to an abundance of moisture it is better to install a cement board as a backer rather than a gypsum board.
At some point along the wall the cement backer board will meet with the drywall used in the rest of the room.