When the FMC gives me the message drag is required that is when I apply the speedbrake. First time message is showing. Next time FMC gives me the message because speed is decreased, I again extend the speedbrake as required this time no message, no alert. Same situation as the first time, but no message of speedbrake extended.  I don't see a difference in this situation. Speed is reduced by FMC and drag is required in both situations, during descent. Thrust in these cases is too high and too fast, so thrust is being reduced.