Start to smoke dope and relax (4,4)
I believe the answer is:
slow down
'relax' is the definition.
(synonyms)
'start to smoke dope' is the wordplay.
'start to' says to take the initial letters.
'dope' becomes 'lowdown' (synonyms).
The first letter of 'smoke' is 's'.
's'+'lowdown'='SLOW-DOWN'
'and' is the link.
(Other definitions for slow down that I've seen before include "Lose velocity" , "Reduce speed" , "relax" , "Don't go so fast" , "take it more easy" .)