Place promoting weight-loss tablet (6)
I believe the answer is:
locale
'place' is the definition.
(I've seen this before)
'promoting weight-loss tablet' is the wordplay.
'promoting weight-loss' becomes 'local' (lo cal, ie low in calories).
'tablet' becomes 'e' (E can mean ecstasy or an ecstasy tablet).
'local'+'e'='LOCALE'
(Other definitions for locale that I've seen before include "Area connected with event" , "Place (of an event)" , "Place associated with particular events" , "Venue" , "Spot" .)