Terribly ill in quarters, squaddie initially gets drugs (14)

I believe the answer is:

tranquillisers

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'drugs' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'terribly ill in quarters squaddie initially' is the wordplay.
'terribly' indicates anagramming the letters.
'initially' suggests taking the first letters.
The first letter of 'squaddie' is 's'.
'ill'+'in'+'quarters'='illinquarters'
'illinquarters' anagrammed gives 'tranquilliser'.
'tranquilliser'+'s'='TRANQUILLISERS'

'gets' is the link.

Can you help me to learn more?

(Another definition for tranquillisers that I've seen is " shifting drugs".)

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