"Cooked" as what?
20 mgs of Ritalin at once (assuming it's the normal tablets, not the LA or SR versions) should be enough to catch a mild but enjoyable buzz for someone who's not a recreational stim user, yes.
'Cooked' is a term I use to explain a alterered state of mind, mostly after consuming weed but it also applies to other drugs.
and they're the normal 10mg tables and I have had no prior Ritilan use.