Dummy swallowed plant with bad smell (7)
I believe the answer is:
placebo
'dummy' is the definition.
(ineffective or dummy version of a drug)
'swallowed plant with bad smell' is the wordplay.
'swallowed plant with' becomes 'place' (I am not sure about this - if you are sure you should believe this answer much more).
'bad smell' becomes 'bo' (body odour).
'place'+'bo'='PLACEBO'
Can you help me to learn more?
(Other definitions for placebo that I've seen before include "Harmless substance as medicine to sooth patient" , "Dummy pill used in testing the effect of medicines" , "Deliberately ineffective drug" , "Medicine with no effect used in drug trials" , "Ineffective medication" .)