General terms:
* Backlash: A strong negative reaction to something.
* Repercussions: The effects of an action or event, especially the unwelcome ones.
* Ramifications: The possible results of an action or decision.
* Aftermath: The consequences or effects of an event, especially a negative one.
* Fallout: The unpleasant results of an event or situation.
* Blowback: Unforeseen and negative consequences of an action.
* Collateral damage: Unintended harm to people or things.
More specific terms:
* Side effects: Unintended consequences of a medical treatment or drug.
* Drawbacks: Disadvantages or problems associated with something.
* Complications: Problems that arise during a process or situation.
* Setbacks: Delays or reverses in progress.
* Disasters: Catastrophic events with serious negative consequences.
The best word to use will depend on the specific context.