Promoters of health spa finally stop (4)
I believe the answer is:
whoa
'stop' is the definition.
(I've seen this before)
'promoters of health spa finally' is the wordplay.
'promoters of health' becomes 'WHO' (World Health Organisation).
'finally' indicates one should take the final letters.
The last letter of 'spa' is 'a'.
'who'+'a'='WHOA'
(Other definitions for whoa that I've seen before include "Opposite of "Giddy-up!"" , "horsy expression?" , "halt" , "Command to horse to stop or stand still" , "Danger" .)