1. Humira

Humira faced its first U.S. biosimilar challengers in mid-2019. (AbbVie)

Company: AbbVie
2019 sales: $19.73 billion
Projected 2026 sales: $6.83 billion
Projected CAGR: -14%
Used for: rheumatoid arthritis, polyarticular juvenile idiopathic arthritis, psoriatic arthritis, ankylosing spondilitis, Crohn's disease, hidradenitis suppurativa, ulcerative colitis, plaque psoriasis

Another year, another run at the top of the sales chart for AbbVie's megablockbuster anti-TNF immunology med Humira. But like all good things, Humira's run at the top could soon meet its end at the hands of biosimilar challengers and a stable of other blockbuster drugs hunting its spot. 

In 2019, Humira hit $19.73 billion in sales for AbbVie in what will almost certainly be the drug's zenith. Biosimilars have already hit in Europe, and AbbVie is expecting U.S. copycats to storm stateside sales beginning in 2023.

All of that competition could drop Humira to $6.83 billion in sales in 2026, according to Evaluate Pharma. That's nothing to sneeze at but still a shadow of the drug's peak. 

Keeping Humira humming until that 2023 cliff will be crucially important for AbbVie as it works to successfully digest Irish drugmaker Allergan after a $63 billion merger completed in May. 

RELATED: AbbVie, Allergan score FTC approval for $63B merger with one final hurdle left to go

1. Humira