Medicine's rapidly recalled over dangerous substance (7)

I believe the answer is:

arsenic

I'm a little stuck... Click here to teach me more about this clue!

'dangerous substance' is the definition.
'arsenic' can be an answer for 'substance' (arsenic is a kind of substance). I'm not certain of the 'dangerous' bit.

'medicine's rapidly recalled over' is the wordplay.
'over' indicates a hidden word (the clue contains or goes 'over' the answer).
'recalled' says the letters should be written in reverse (to recall can mean to bring something back).
'cinesra' is hidden within 'medicines rapidly'.
'cinesra' back-to-front is 'ARSENIC'.

Can you help me to learn more?

(Other definitions for arsenic that I've seen before include "Element with many poisonous compounds" , "-- and Old Lace (play)" , "Ratsbane" , "Brittle grey-green semi-metal, atomic number 33" , "Powerful poison" .)

I've seen this clue in The Telegraph.

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