Trip facilitator has setter endlessly climbing (8)
I believe the answer is:
mescalin
'trip facilitator' is the definition.
(drug that might give you a trip)
'setter endlessly climbing' is the wordplay.
'setter' becomes 'me' (the setter of the clue).
'endlessly' means to remove the last letter.
'climbing' becomes 'scaling' (scaling is a kind of climbing).
'scaling' with its final letter taken off is 'scalin'.
'me'+'scalin'='MESCALIN'
'has' is the link.
(Other definitions for mescalin that I've seen before include "Hallucinatory drug" , "Peyote hallucinogen" , "Cactus hallucinogen" , "Drug from peyote cactus" , "what makes a trip" .)