If ritalin (methylphenidate) is the same as cocain in many ways, then does it cause serious brain damage ? like killing brain cells.

It depends.: Ritalin or methylphenidate is a stimulant like cocaine. If taken improperly, it may have injurious effects to the brain. If taken as prescribed, then it should create minimal problems and in fact help you focus by stimulating the frontal cortex involved in finishing tasks and paying attention. Side effects include elevated blood pressure, tachycardia, insomnia and mild loss of appetite.