Bring law in to drop sugar (7)
I believe the answer is:
lactose
'sugar' is the definition.
(I know that lactose is a type of disaccharide)
'bring law in to drop' is the wordplay.
'bring law' becomes 'act' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' indicates putting letters inside.
'to drop' becomes 'lose' (I've seen this in other clues).
'act' put within 'lose' is 'LACTOSE'.
Can you help me to learn more?
(Other definitions for lactose that I've seen before include "Constituent of milk" , "White substance in milk" , "Sugar found in milk" , "A sugar present in milk" , "Part of milk" .)