1. Humira
The companies: AbbVie, Eisai
Worldwide sales: $11.02 billion

AbbVie ($ABBV) rides Humira sales hard; the anti-inflammatory drug has churned out the majority of the company's revenue since Abbott Laboratories ($ABT) spun it off last January. In AbbVie's first full year on its own, its $10.7 billion from Humira made up 57% of overall sales, which tallied $18.8 billion.

Luckily for AbbVie, Humira's growth has shown no signs of slowing. Thanks to a score of additional indications as a treatment for ailments the likes of plaque psoriasis, Crohn's disease and ulcerative colitis, sales have nearly doubled since 2010's $5.5 billion haul. And in 2013 alone, Humira posted double-digit gains each quarter for AbbVie, with revenue increases from the year-ago period coming in at 16%, 13%, 19% and 13% in Q1, Q2, Q3 and Q4, respectively.

But no drug can stay at the top forever; Humira's patent protection is set to expire in 2016. And somewhat unsurprisingly, Humira's success has put a target on its back for biosimilar developers hungry for a piece of its revenues. A recent report from Moody's named AbbVie's drug as among the most sought-after prototypes for biosimilar copies; Novartis' ($NVS) Sandoz, for one, is well on its way with a version, starting Phase III trials in mid-December.

But until copycats hit, AbbVie plans to keep things going in the same direction. The company expects $19 billion in 2014 revenue, with Humira sales figuring in heavily.

For more:
Special Report:Top 10 rheumatoid arthritis drugs 2013
More Humira sales gains help AbbVie meet forecasts
Humira sales, up 19%, continue to carry AbbVie
Humira stays strong for AbbVie as drugmaker scrambles for new offerings

-- Carly Helfand (email | Twitter)