Mom has been on Namenda for 8/9 yrs. She struggles taking meds and was displaying memory issues taking Namenda. Thoughts on weaning her off?

Her Dr. definitely knows. Mom takes a few over the counter meds but just really struggles with taking them. We really didn't feel that the Namenda was helping her so that's why my sister, an RN was going to slowing wean Mom off. In all my reading I never see what the consequences of that might be. Thanks for your help!