Figure prat out, one for some drug-users to avoid (10)

I believe the answer is:

grapefruit

I'm a little stuck... Click here to teach me more about this clue!

'one for some drug-users to avoid' is the definition.
I can't tell whether this defines the answer.

'figure prat out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'figure'+'prat'='figureprat'
'figureprat' with letters rearranged gives 'GRAPEFRUIT'.

Can you help me to learn more?

Want a hint initially instead of a full solution? Install my app