The French feel effects of hallucinogenic drugs and don’t hold back (3,3)
I believe the answer is:
let rip
'hallucinogenic drugs and don't hold back' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'the french feel effects' is the wordplay.
'the french' becomes 'le' ('the' in French).
'feel effects' becomes 'trip' (I can't justify this - if you can you should believe this answer much more).
'le'+'trip'='LET RIP'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for let rip that I've seen before include "Go wild" , "Express oneself without restraint" , "Talk aggressively" , "Act unrestrainedly" , "Abandon restraint - allow to tear" .)