It depends on a couple of things. First, how far down is the ceiling suspended? If it's less than 16-inches, then any reflected sound in the cavity above is amplified which will be a problem. Second, what are the tiles made of? If they are thin cheap fiberboard, then they will transmit sound above (resulting in the same problem as above) plus reflect sound back down in the room. Third, what's the ceiling height? Less than 9-feet could be a problem with early reflections. However, if your ceiling is suspended 16 to 18-inches, the tiles have decent sound absorption and is 9-feet or more above the floor then you have an advantage over a hard, flat untreated ceiling.
The best way to treat a suspended ceiling is to roll insulation (without foil scrim or face) above it. The thicker the insulation, the better. BTW, structural limitations take priority. Also, if there are flourescent lights with flat acrylic lenses, you should consider replacing them with parabolic lensed troffers. Much better sound diffraction.