Increasing findings suggest that different components of the stimulus-response pathway (perceptual, motor or cognitive) may account for slowed performance in Multiple Sclerosis (MS). It has also been reported that depressive symptoms (DS) exacerbate slowness in MS. However, no prior studies have explored the independent and joint impact of MS and DS on each of these components in a comprehensive manner. The objective of this work was to identify perceptual, motor, and cognitive components contributing to slowness in MS patients with and without DS. The study includes 33 Relapsing-Remitting MS patients with DS, 33 without DS, and 26 healthy controls. Five information processing components were isolated by means of ANCOVA analyses applied to five Reaction Time tasks. Perceptual, motor, and visual search components were slowed down in MS, as revealed by ANCOVA comparisons between patients without DS, and controls. Moreover, the compounding effect of MS and DS exacerbated deficits in the motor component, and slowed down the decisional component, as revealed by ANCOVA comparisons between patients with and without DS. DS seem to exacerbate slowness caused by MS in specific processing components. Identifying the effects of having MS and of having both MS and DS may have relevant implications when targeting cognitive and mood interventions.