What is the difference between Mephedrone and methadone?

i know Mephedrone is legal and that Methadone is a class a drug, but what is the difference.
im going to feel like a noob, but i've done Mephedrone and was wondering if its anything like Methadone

: http://alcoholdrugstreatment.info/what-is-the-difference-between-mephedrone-and-methadone