My Mother Is 90 & Has Had Parkinsons For Two

My mother is 90 & has had Parkinsons for two years for which she takes Sinemet. Her Parkinsons symptoms of tremors & shuffling gait are very well controlled, but she is also starting to exhibit some "combative" behavior along with other cognitive issues. When my dad had these symptoms (no Parkinsons), Namenda was very helpful. Does this drug have any untoward effects with Sinemet?