Arbitration about 100 drugs (10)
I believe the answer is:
medication
'arbitration about 100 drugs' is the definition.
I can't tell whether this defines the answer.
'arbitration about 100' is the wordplay.
'arbitration' becomes 'mediation' (synonyms).
'about' means one lot of letters goes inside another.
'100' becomes 'C' (Roman numeral).
'mediation' going around 'c' is 'MEDICATION'.
Can you help me to learn more?
(Other definitions for medication that I've seen before include "treatment regime" , "drugs etc." .)