1. Humira

AbbVie and Eisai
Rheumatoid Arthritis and other inflammatory conditions
2015 sales: $14 billion
2020 projection: $15.92 billion

Humira, currently the world's best-selling drug, will still be holding onto that title in 2020, EvaluatePharma predicts. Between now and then, though, analysts expect it to hit its peak and then begin its decline. The key questions: When, exactly, will that decline begin? And how fast will it happen?

The answers depend on which analysts you ask. It's no secret that biosimilars are on the way; India's Zydus Cadila already has one on the market in India, and plenty of other knockoff makers wouldn't mind snagging a piece of the med's hefty sales haul. In June, biosimilar industry members, payers, regulators, lawyers and healthcare investors who participated in a survey conducted by Bloomberg Intelligence predicted Humira biosims would be the most successful copycat biologics launched in the U.S. and Europe.

AbbVie, though, has touted its robust stateside IP protection, which it claims will keep rivals off the U.S. market until 2020. As Suntrust analyst John Boris sees it, the company will have time to extract "maximum value" from the franchise through volume gains, pricing, label expansion, a new formulation, etc.--all "well before" biosimilars hit.

Citi analyst Andrew Baum sees things differently, though. Humira sales will take a hit beginning in 2018, he predicted in a February note to clients, with the med's revenues declining from $16 billion at their peak in 2017 to $6 billion in 2022.

AbbVie is trying to soften the blow through M&A and new products. The company in 2014 shelled out $21 billion for Pharmacyclics to get its hands on the drugmaker's share of blood cancer powerhouse Imbruvica. And analysts are predicting big things from AbbVie's new hep C med Viekira Pak, which could potentially break the blockbuster barrier.

New indications could also help Humira on the rocky road ahead. AbbVie recently snagged European approval for a new formulation of the drug to reduce pain from injections. In September 2015, the company scored a win after the FDA approved Humira to treat a rare inflammatory skin disease--an indication with peak-year sales potential of $1 billion annually, Scott Brun, AbbVie's VP of pharmaceutical development, told FiercePharma at the time of the approval.

AbbVie plans to keep the regulatory wheel churning for Humira, he added, planning to submit applications in the U.S. and EU in 2015 for Humira to treat inflammatory eye diseases. Those indications, along with 9 other approved indications in the U.S., make the drug "well-positioned to face the challenges of potential new entrants," Brun said. --Carly Helfand (email | Twitter) and Emily Wasserman (email | Twitter)

For more:
Strong Q4 showings for AbbVie abroad offset Humira, Viekira stumbles at home
Amgen's Humira biosim is one step closer to FDA approval. But how close is it to market?
Humira gives AbbVie solid Q3 support, but biosimilars loom
Baxalta joins biosim makers eyeing a piece of AbbVie's Humira

1. Humira