Regressing predictably involves this drink (5)
I believe the answer is:
cider
'this drink' is the definition.
(cider is a kind of drink)
'regressing predictably involves' is the wordplay.
'regressing' is a reversal indicator (to regress is to go backwards).
'involves' says the answer is hidden in the clue.
'redic' is hidden within 'predictably'.
'redic' in reverse letter order is 'CIDER'.
(Other definitions for cider that I've seen before include "Beverage from apple juice" , "Alcohol from apples" , "Alcoholic drink from fermented apple juice" , "Alcoholic drink (to be taken with Rosie?)" , "Pear drink" .)