What causes clogged milk duct when weaning?

Slow flow: Although clogged milk ducts can occur anytime during breast feeding, it is more common whenever the flow of the milk slows down and the milk is not emptying as regularly. This happens more frequently during weaning. It may help to warm pack the area that is clogged, and massage of that area can also be very beneficial, albeit sometimes initially painful. As supply drops, it will be less of a prob.