Fatigued when restricting Ecstasy in ranks (6)
I believe the answer is:
tiered
'in ranks' is the definition.
(I've seen this before)
'fatigued when restricting ecstasy' is the wordplay.
'fatigued' becomes 'tired' ('tired' can be similar in meaning to 'fatigued').
'when restricting' indicates putting letters inside.
'ecstasy' becomes 'e' (informal term for the drug).
'tired' placed around 'e' is 'TIERED'.
(Other definitions for tiered that I've seen before include "Constructed in layers, like wedding cake" , "Laid out in layers, like wedding cake" , "Cunstructed in layers" , "Built in layers" , "Arranged in layers like big cake" .)