Gilead Sciences Inc. achieved a scientific breakthrough when it developed a cure for hepatitis C, the viral infection that can have severe and deadly complications.

The company’s biggest problem these days appears to be that it works.

Gilead GILD, -0.92% shares sunk 9.7% in heavy volume Wednesday morning after the company issued 2017 sales guidance far below even reduced Wall Street expectations.

“We believe investors expected guidance to be light... just not necessarily this light,” said J.P. Morgan analyst Cory Kasimov.

Company executives were frank as to the reasons why: “Our expectation is that patient starts in 2017 will be lower than in 2016” for Gilead’s key hepatitis C franchise, said Chief Operating Officer Kevin Young.

Last year’s patient counts were lifted by new access to two large U.S. health insurers and more patients treated through the VA, he said.

But Gilead isn’t likely to benefit again from those this year, he said.

A changing patient population is also expected to stymie revenue growth, he said: Patients with less advanced forms of hepatitis C, for whom there will be less urgency to use the company’s pricey medications, and patients with other reasons to delay medication use, such as other simultaneous medical conditions, ongoing drug or alcohol use and unstable living situations.

Related: Gilead revenue falls as hepatitis drug sales drop

The effect is visible in the U.S. but is expected to move and “fast” to other countries, including Germany, France and the United Kingdom, Young said.

Though Gilead’s HIV franchise should power some growth, there aren’t many new launches coming out in the next few years and patents are expiring on some products, including hepatitis B medication Viread, said Chief Executive Officer John Milligan.

Management named lower-than-expected hepatitis C market share and slower-than-expected HIV franchise growth as among the uncertainties affecting guidance.

See: All eyes will be on Gilead’s hepatitis C franchise as it reports fourth-quarter earnings

On the company’s earnings call, leadership insisted that 2017 guidance wasn’t too conservative. But some are still holding out hope.

Revenue guidance “does appear perhaps conservative given all the unknowns for the year and history suggests they tend to start pretty conservative at [the] start of the year,” said RBC Capital Markets analyst Michael Yee.

With sales flagging, the focus on Wall Street has shifted to potential merger and acquisition activity. But analysts, reading into the year’s guidance, see plenty of reasons to be concerned.

Gilead will need to do three or four deals below about $20 billion and meet expectations over the next two quarters to regain its stock strength, said Yee.

Related: This is the most expensive drug in America

Kasimov said he was maintaining an overweight rating for Gilead, although “our frustration on the lack of a clearly articulated strategy continues to grow.”

Though many pharmaceutical companies stand to be affected by the uncertainty around the Affordable Care Act, Gilead is especially so, with many state and federal programs picking up the tab for its key medications.

“The company’s current risk is accentuated by challenges to their US market sales from public insurance repeal or reform, from patent expiries over the next 18 months, and from new and potentially disruptive competitors in their two leading therapeutic categories,” said Leerink analyst Geoffrey Porges, who maintained a market perform rating and reduced price target by nearly 20% to $74.