Hi there. I didn't hear of such thing and among the mummies in my chat group 9+ was a v popular model and a few of my friends and I also using it. It did not make our supply drop but u have to know that it is not as powerful at the S1 which is a hospital grade. So if u compare the "suction" u use for S1 and S9, u have to use 1-2 level higher. If use the same level of suction, it can take longer to empty the boobs - then some pple pump by "time spent pumping" so they pump lesser out and then the supply will drop. So as long as u adjust the suction high enough, u will be able to get out the same amount of milk in the same time frame. With that in mind then u are safe :)