I don't know, but I have never come across any reference to say that magnesium citrate contracts the gallbladder in the same way as magnesium sulphate does. However, Magnesium has the ability to relax smooth muscles and I would assume the sphincter of Oddi but this may not necessarily result in the dilation of the common bile duct which is dependant upon an increase in biliary pressure, usually provided by the gallbladder contraction.