1. Gilead Sciences

Gilead's current and future success lies in the hands of its antiviral franchise. That franchise, led by its hepatitis-C cures Sovaldi and Harvoni, accounted for roughly 60% of the company's total product sales revenue in 2015. Analysts, however, are concerned that Harvoni's sales may already have peaked. The company anticipates 230,000 U.S. patient starts in 2016, representing an 8% decline from 2015. Looking forward, Gilead plans to tackle another liver-attacking disease: nonalcoholic steatohepatitis, also known as nonalcoholic fatty liver disease, which affects 2% to 5% of Americans. On the deal-making front, the drugmaker acquired Nimbus Apollo, a subsidiary of Nimbus Therapeutics, in April. The deal was worth up to $1.2 billion and netted Gilead Nimbus Apollo's lead experimental treatment for NASH, ACC inhibitor ND1-010976. Gilead also saw the recent approval of Descovy, a fixed-dose combination for the treatment of HIV. Descovy has similar efficacy to Viread — another Gilead HIV treatment — but at one tenth the dose. This drug is expected to give providers more flexibility in dosing for patients, as it's often paired with other antiretrovirals in an HIV regimen.