Suggested Sid and Dave are involved (7)
I believe the answer is:
advised
'suggested' is the definition.
('advise' can be a synonym of 'suggest')
'sid and dave are involved' is the wordplay.
'and' means one lot of letters go next to another.
'are involved' indicates anagramming the letters (involved can mean confusing or complex).
'sid' put after 'dave' is 'davesid'.
'davesid' with letters rearranged gives 'ADVISED'.
(Other definitions for advised that I've seen before include "Warned" , "Given recommendation" , "Notified" , "Informed" , "Gave guidance to" .)