Fit to swallow tablet pro tem (7)
I believe the answer is:
'pro tem' is the definition.
(both can mean temporary)
'fit to swallow tablet' is the wordplay.
'fit' becomes 'in trim' (in trim means healthy or fit).
'to swallow' means one lot of letters goes inside another.
'tablet' becomes 'e' (E can mean ecstasy or an ecstasy tablet).
'intrim' going around 'e' is 'INTERIM'.
(Other definitions for interim that I've seen before include "Meanwhile" , "Stopgap" , "Meantime - provisional" , "not there for ever" , ", I'm put in grave situation initially" .)