Are the medications prescribed to delay memory loss for people with dementia really effective and are they often accompanied by side effects (diarrhea, etc.)?

My aunt has had dementia for 5 years and was diagnosed about 4 years ago. Her doctor has just suggested that she be prescribed a drug to delay memory loss. She took a cognitive test and scored 9 out of 30. In just a few minutes, she can't remember what she was told or what she might have done or what might have happened to her (for example, if she fell and hurt herself). She lives in a residence for independent seniors and is able to dress herself, make herself breakfast, go to the dining room and participate in some activities.

Merci.