OoP: What was wrong with Sirius theory

[lily_paige_delaney]

No: HPFGUIDX 65613

I was re-reading OoP and last night noticed something I didn't see 
first time around and I don't think it is cleared up in the book 
(apologies if I'm wrong).

Ch 18 - Dumbledore's Army pg. 340

Harry is falling asleep whilst reading about the uses of scurvy 
grass, lovage and sneezwort.

"These plantes are moste efficacious in the inflaming of the braine, 
and are therefore much used in Confusing and Befuddlement draughts 
where the wizarrd is desirous of producing hot headedness and 
recklessness."

Harry starts to make the connection with Sirius' behaviour and state 
of mind but then falls asleep and I don't think it gets mentioned 
again.

My first reaction was that Kreacher must have been slipping him the 
potion and that is why Sirius was so happy at Christmas - because 
Kreacher wasn't there.  I still think this is true, however, who 
brewed the potion? - our dear potions master?? or someone else 
within the Order?  Also doesn't this behaviour sound a bit like 
Harry's throughout the book too.  

LPD