Change popular recreational drug for opiate (8)

I believe the answer is:

morphine

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'opiate' is the definition.
(thesaurus)

'change popular recreational drug' is the wordplay.
'change' becomes 'morph' (morphing is a kind of changing).
'popular recreational drug' becomes 'ine' (I can't explain this - if you can you should believe this answer much more).
'morph'+'ine'='MORPHINE'

'for' acts as a link.

Can you help me to learn more?

(Other definitions for morphine that I've seen before include "Pain-easing opiate" , "Pain-killing drug" , "Sedative derived from opium" , "Pain-relieving opiate" , "Powerful pain-reliever" .)

I've seen this clue in The Independent.

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