On the up side, 2 years of taking Repatha along with conventional statins reduced LDL, the bad cholesterol, from 92 to 30.
And side effects were similar to a dummy drug.
However, at more than $14,000 a year, Repatha still has insurers balking, especially without proof it actually reduces heart incidents, not just cholesterol numbers.
The new study, published in the New England Journal of Medicine, offers some evidence, however, not as big a benefit as some doctors had hoped.
For every 200 people treated with Repatha for roughly two years, three fewer people would suffer a heart attack, stroke or heart-related death.
But looked at by themselves, deaths were not reduced by the drug.
Dr. Donald Lloyd-Jones, preventive medicine chief at Northwestern University and an American Heart Association spokesman, called the results modest and "not quite what we hoped or expected."
Dr. Mark Hlatky, a Stanford University cardiologist and cost effectiveness researcher, said, "people were hoping for a breakthrough, a lot bigger result than 20 percent."
Statins such as Lipitor and Crestor are cheap and lower LDL or bad cholesterol, but some people can't tolerate or get enough help from them.
Amgen's Repatha, is given as a shot once or twice a month and is part of a novel class of medicines called PCSK9 inhibitors that drop LDL to unprecedented levels.
Repatha and a similar drug, Praluent, were approved in 2015 for people with inherited risk for high cholesterol, or heart disease that had already caused a problem such as a heart attack.
Dr. Hlatky says the biggest issue is whether the cut heart attacks and strokes enough to be worth the higher price.
If they cost 50 times as much as statins, "are they 50 times better? I don't think so," said Hlatky.
For now, "we should still probably reserve these for the highest risk patients where statins are not doing a good enough job - at least at the price they are currently offered," said Lloyd-Jones.
Amgen said the drug's value justifies its cost, and offered more deals for insurers, including refunds for people who have a heart attack or stroke after using Repatha for at least six months.
A study testing whether Praluent also lowers heart risks will wrap up later this year. The companies also are in a patent war over the drugs.
How do insurance companies decide what medicines to pay for and when to pay for them?
Insurers and other payers look first at how well the drug works - not its cost - when they decide whether to cover the latest treatments, according to the nation's largest pharmacy benefits manager, Express Scripts.
The price patients eventually pay gets determined later, when an insurance company or pharmacy benefits manager decides where a drug fits on a list of covered treatments called a formulary.
The cost of prescription drugs has become a growing source of concern with doctors and patients, but it's not a factor considered by an independent committee used by Express Script to determine coverage of a new drug, Chief Medical Officer Dr. Steve Miller said.
That committee - 15 doctors and a pharmacist - reviews the information that federal regulators used to approve a drug and then decides whether it should be covered.
Some payer coverage decisions come with qualifications like a requirement that patients meet specific criteria or try other treatments first.
That can limit patient access. Doctors say some patients have had trouble getting a new cholesterol-lowering drug, Repatha, that costs $14,000 a year, because of the restrictions.
Insurers largely use pharmacy benefits managers to set up the lists that determine how much a patient ends up paying.
Some lists are divided into tiers, with drugs on the bottom generally being generic or least expensive.
Those on the highest tier might include specialty medicines that could cost the patient hundreds of dollars even with coverage.
Whether a drug even gets on the list can depend on whether a similar medicine is already in the market.
When the ground-breaking hepatitis C treatments Sovaldi and Harvoni from Gilead Sciences debuted a few years ago, Express Scripts had to include them.
They cost more than $80,000 for a course of treatment, but the drugs essentially cure a debilitating disease and they had no competition.
But once the drugmaker AbbVie produced a third option, Viekira Pak, with a similar cure rate, Express Scripts was able to negotiate a price discount and switched to covering only Viekira Pak.
The nation's two largest pharmacy benefits managers, Express Scripts and CVS Health Corp., both say they cover Repatha.