The widely-expected sale of energy and fruit drinks Lucozade and Ribena could bring in some 1.2 billion pounds($1.8 billion), if the brands sell for twice the value of their annual sales, as some analysts expect.
The surprise move to bundle some established drugs into a new unit, meanwhile, could bring in substantially more. With sales last year of 3 billion pounds, those brands could generate proceeds of 9 billion to 12 billion pounds, said Panmure Gordon analyst Savvas Neophytou.
"Depending on tax implications of that sort of divestment, or spin-out, we may see an increased clamour for a special dividend in coming months," he said. "This should drive further outperformance."
Analysts at Berenberg and Jefferies also said the move was bound to fuel speculation that the business could ultimately be spun out from the group.
The new division housing GSK's established products will include older medicines that are no longer widely promoted, such as stomach acid treatments Tagamet and Zantac, Imitrex for migraine, and anti-nausea treatment Zofran.
The unit will report results separately from January 2014.
Chief Executive Andrew Witty said the creation of the separate business clearly increased the company's options.
"How it might play going forward is an open question," he said after announcing first-quarter results.
"This is a sensible move to ensure we are maximising value in the short run but, of course, it opens up optionality for us in the future."
An outright sale is not the only option. Other possibilities could include selling just some of the products in the unit or placing them into a joint venture with another company, as GSK has done already with its HIV/AIDS drugs via a deal with Pfizer and Shionogi.
($1 = 0.6542 British pounds)
(Reporting by Ben Hirschler; Editing by Elaine Hardcastle)