In 2015, Humira (Adalimumab) represented 61% of AbbVie's total revenues, which could be seen as problematic since the composition of matter patent covering Humira expires in December 2016 in the U.S., and in October 2018 in the European Union. However, Humira is covered by more than 50 other patents on formulation, method of treatment, manufacturing and more. Those other patents are due to expire between 2022 and 2034, which should make it more difficult for competitors to come up with biosimilar versions of Humira.Either way, AbbVie is going to start experiencing competition from other companies that are more than capable of producing Humira biosimilars - the technology to produce therapeutic antibodies is becoming more and more commonplace, and even large academic groups are jumping on the bandwagon. This means that, as far as technical complexity goes, making a biosimilar is within the capability of a talented PhD student.
What I think the market is over-estimating is the ability for competing biosimilars to carve out Humira market share, probably with the assumption that customers will be able to substitute one antibody for another as easily as one proprietary molecule for a generic drug in the small molecule drug space.
Unfortunately, it's not that easy. Antibodies can have a ton of idiosyncratic activities; they're bigger, and less well defined than small molecule drugs. In addition, there's going to a great deal of brand name inertia with Humira, as consumers stick with what works until a generic proves that it's as good as the original - which will take some time. This likely means that Abbvie can ride out the storm and plan a strategy to protect this drug for a little while longer.