How much brain damage can the drug ecstasy do?

I'm curious to know about this drug. How much brain damage can it do and how serious are the side effects? I've heard of stores about ravers turning into "E-tards", which is a paraody of retard. Can someone explain this to me?

: http://alcoholdrugstreatment.info/how-much-brain-damage-can-the-drug-ecstasy-do