The thickest hooligan loses the head and takes drugs in race (8)

'the thickest hooligan loses the' is the definition.
I can't judge whether this defines the answer.

'head and takes drugs in race' is the wordplay.
'head' becomes 'ob' (I can't explain this - if you can you should believe this answer much more).
'and' means one lot of letters go next to another.
'takes drugs' becomes 'uses' (someone who takes drugs is a 'user').
'in' means one lot of letters goes inside another.
'race' becomes 'tt'.
'uses' put into 'tt' is 'tusest'.
'ob'+'tusest'='OBTUSEST'

Can you help me to learn more?