Confuse; go off (5)
I believe the answer is:
addle
This clue is a double definition.
'confuse' is the first definition.
(I know that addle is a type of confuse)
'go off' is the second definition.
(eg an egg might addle)
(Other definitions for addle that I've seen before include "Get confused" , "(Of eggs) turn bad" , "Mix up or confuse" , "Make rotten" , "(Of egg) become rotten" .)