adline,

I just read another post that linked to an article on Adderall XR. Judging by the graph on the page, Adderall XR is supposed to work exactly as you describe: A 20mg dose of Adderall XR should be equivalent to two 10mg doses of regular Adderall spaced 4 hours apart.

Here's the graph:


Here's the page:
http://rxlist.com/cgi/generic3/adderallxr_cp.htm

And here's the other post I got this all from:
http://forums.psychcentral.com/showf...=318577&Forum=,All_Forums,&Words=adderall%20xr&Searchpage=1&Limit=25&Main=309012&Search=true&where=sub&Name=&daterange=1&newerval=10&newertype=y&olderval=&oldertype=&bodyprev=#Post318577