When Flymo's final component is absent, squash up grass, perhaps (4)

I believe the answer is:

drug

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'grass perhaps' is the definition.
(I know that Mary Jane is a type of cannabis)

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for drug that I've seen before include "may be soft or hard" , "Medical or narcotic substance" , "Perhaps grass" , "Sedate" , "Pharmaceutical (or recreational) item" .)

I've seen this clue in The Telegraph.

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