Novo Nordisk ( NVO 0.33%) stock jumped 3.1% at the open Thursday morning before drifting back. As of 10:54 a.m. ET, it was still up by about 1.2%.

The deal could expand access to its in-demand obesity drug at the expense of Eli Lilly, whose shares fell by double digits on Thursday.

The U.K.'s FTSE 100 moved between losses and gains on Thursday, with most other European markets closed for the May 1 holiday.The FTSE 100 was flat at 12:34 p.m. in London after notching its 13th straight positive session in its longest winning run since late 2016 into early 2017.