Long without drugs, initially ecstasy, not allowing a fix? (14)
I believe the answer is:
indeterminable
'not allowing a fix?' is the definition.
(something indeterminable is not fixed or certain)
'long without drugs initially' is the wordplay.
'long' becomes 'interminable' (similar in meaning).
'without' indicates putting letters inside ('without' can be similar in meaning to 'outside').
'drugs initially' becomes 'de' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'interminable' going around 'de' is 'INDETERMINABLE'.
'ecstasy' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
(Another definition for indeterminable that I've seen is " can't be settled".)