The description of the dissonant whispers spell says (PHB, p. 234):
On a successful save, the target takes half as much damage and doesn't have to move away.
Does this mean that the target can still choose to use this opportunity to use its reaction to move away?
This is especially important if the target has feature that prevents opportunity attacks and prefer to attack at range.
Best Answer
The target of Dissonant Whispers may take a reaction to move away.
Dissonant Whispers "allows" you to take a reaction:
A failed save leaves you no option to not be forced to spend your reaction. If you succeed you may choose not to take that reaction or to take that reaction trigger that the spell grants you - as long as you have a reaction available.