Obsessive helping to make designer drugs (4)

I believe the answer is:

nerd

'obsessive' is the definition.
(nerd can mean an obsessive)

'helping to make designer drugs' is the wordplay.
'helping to make' indicates the answer is hidden within the clue.
'NERD' is hidden within 'designer drugs'.

(Other definitions for nerd that I've seen before include "Socially inept but knowledgeable person" , "one that's overly cerebral" , "Feeble person (sl.)" , "Computer geek?" , "Flag on poles; wide (headline)" .)

I've seen this clue in The Times.

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