Menace Tehran perhaps, taking time and energy (8)
I believe the answer is:
threaten
'menace' is the definition.
('threaten' can be a synonym of 'menace')
'tehran perhaps taking time and energy' is the wordplay.
'perhaps' indicates anagramming the letters.
'taking' is an insertion indicator.
'time' becomes 't'.
'and' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'tehran' with letters rearranged gives 'threan'.
't'+'e'='te'
'threan' placed around 'te' is 'THREATEN'.
(Other definitions for threaten that I've seen before include "Utter menaces" , "Look likely to" , "Give warning of something unpleasant" , "Impend, portend" , "Utter intentions of injury or punishment" .)