Doctors injecting drug, a thousand get hallucinations (6)
I believe the answer is:
dreams
'hallucinations' is the definition.
The answer and definition can be both related to thinking as well as being plural nouns.
Maybe there's an association between them I don't understand?
'doctors injecting drug a thousand' is the wordplay.
'doctors' becomes 'drs' ('Dr' can be a synonym of 'doctor').
'injecting' is an insertion indicator.
'drug' becomes 'e' (e is another name for ecstasy).
'a thousand' becomes 'am' (I can't explain this - if you can you should give a lot more credence to this answer).
'e'+'am'='eam'
'drs' enclosing 'eam' is 'DREAMS'.
'get' acts as a link.
Can you help me to learn more?
(Other definitions for dreams that I've seen before include "Imaginings" , "Fantasies; fantasises" , "'We are such stuff / As dreams are made on' (The Tempest)" , "'''We are such stuff as ... are made on'' The Tempest (6)'" , "Thoughts and visions during sleep" .)