Designer drug cut with crushed silica (11)

I believe the answer is:

specialised

'designer' is the definition.
(designer can mean specialised or branded)

'drug cut with crushed silica' is the wordplay.
'drug' becomes 'speed' (speed is a kind of drug).
'cut with' means one lot of letters goes inside another.
'crushed' indicates an anagram.
'silica' with letters rearranged gives 'cialis'.
'speed' enclosing 'cialis' is 'SPECIALISED'.

(Another definition for specialised that I've seen is " Concentrating on one subject".)

I've seen this clue in The Independent.

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