There are several good answers for the crossword clue “contrary in effect” depending on the number of letters required:
7 Letters:
- DEFEAT (can imply the opposite of achieving a desired effect)
- HAMPER (to hinder or obstruct progress)
- NEGATE (to cancel out or make ineffective)
- REVERSE (to cause something to go in the opposite direction)
8 Letters:
- BACKFIRE (when an action has the opposite of the intended effect)
- COUNTERACT (to oppose or neutralize the effect of something)
- DERAIL (to cause something to fail or be stopped)
- SUBVERT (to undermine or turn something to a different purpose)
Other options (depending on the specific number of letters required by the clue):
- UNDO (4 letters)
- OFFSET (6 letters)
- THWART (6 letters)
The best answer depends on the specific number of letters in the crossword puzzle. If you can provide that information, I can narrow down the options further.