Happines giving berries?

Question

When you give a happines giving berry to your Pokemon how much EVs does it lower?

can you train them back?

here's more explanation because I might as well not gave much anyways whn you give a happines giving poffin it says it increases happines but lowers a stat I noticed it reduces EVs and thats where the too questions enter

Answer 1

>Most of the Generation IV EV system remains unchanged from Generation III. However EV-reducing berries will reduce Effort Points to 100 if the current Effort Points for the stat were above 100

~Bulbapedia (I can't link it to you because I am using my 3DS atm)

You can train them back or train a stat that hasn't been maxed out yet. However using these berries can be tricky as you wouldn't like to use the wrong berry and lower a stat drastically to find yourself training it from scratch
However it is certainly possible :)