Perform Saturday with media boss, medicated (5)
I believe the answer is:
dosed
'medicated' is the definition.
(dosing is a kind of medicating)
'perform saturday with media boss' is the wordplay.
'perform' becomes 'do' (both can mean complete an action).
'saturday' becomes 's'.
'with' says to put letters next to each other.
'media boss' becomes 'ed' (short for editor).
'do'+'s'+'ed'='DOSED'
(Other definitions for dosed that I've seen before include "Given medicine" , "Administered a drug to" , "Given a drug" , "Given shot" , "Gave medicine to" .)