Possibly free herbal extract in a cigarette (6)
I believe the answer is:
reefer
'a cigarette' is the definition.
(I've seen this before)
'possibly free herbal extract' is the wordplay.
'possibly' indicates anagramming the letters.
'herbal extract' becomes 'er' (I can't justify this - if you can you should give a lot more credence to this answer).
'free' with letters rearranged gives 'reef'.
'reef'+'er'='REEFER'
'in' is the link.
Can you help me to learn more?
(Other definitions for reefer that I've seen before include "A sailor's jacket or marijuana cigarette" , "Unofficial smoking" , "refrigerated transport" , "Easy" , "Canvas trimmer" .)