Heroin in the morning? Well over the top (5)

I believe the answer is:

hammy

'over the top' is the definition.
(as in hammy acting)

'heroin in the morning? well' is the wordplay.
'heroin' becomes 'H' (H is a slang term for heroin).
'in the morning?' becomes 'am' (short for ante meridiem - before noon).
'well' becomes 'my' (both are expressions of surprise).
'h'+'am'+'my'='HAMMY'

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.