WASHINGTON (AP) – Federal health officials said Friday a blood thinner from Eli Lilly offers life-saving benefits over drugs currently on the market, though its use may have to be restricted due to bleeding side effects.

The Food and Drug Administration is reviewing the highly anticipated drug, called prasugrel, as a therapy for patients with acute heart problems such as heart attacks, who face increased risk of blood clots. Lilly developed the drug with Japanese drugmaker Daiichi Sankyo.

In a 357-page review posted online, FDA reviewers said the drug’s effectiveness over the leading blood thinner Plavix “seems beyond question.” Plavix, the second-best-selling prescription medicine in the world, is made by Bristol-Myers Squibb and Sanofi-Aventis. Like Plavix, pragrusel works by stopping components of blood, called platelets, from sticking together and clotting.

Regulators have delayed making a decision on prasugrel twice since it was submitted last January. Analysts have attributed much of the delay to prasugrel’s unusual safety profile: while it clearly reduces life-threatening heart problems, it also increases risk of internal bleeding.

Next week the agency will ask a panel of outside cardiology experts to assess the drug’s risks and benefits.

The FDA typically follows its experts’ advice, though agency reviewers already backed approval for the drug in their assessment Friday, saying its lifesaving benefits outweigh its side effects.

Data from a 12-month study reviewed by FDA showed that for every 24 serious heart problems the drug prevented, it caused 10 bleeding side effects. Overall, reviewers concluded that prasugrel was associated with three fewer heart-related deaths than Plavix.

“The division believes that this is a worthwhile risk-benefit profile for patients who might receive prasugrel,” the agency states.

Reviewers also mentioned increased rates of cancer seen in patients taking prasugrel, compared with Plavix. However, the agency notes that the drug’s internal bleeding side effect may have simply led to more medical exams and higher detection of existing cancers.

Indianapolis-based Lilly made this point in its own briefing documents posted Friday.

“We feel like we’ve investigated this issue very carefully, and there’s no scientific evidence that prasugrel causes new cancer or makes an existing cancer worse,” Eli Lilly Vice President Dr. Anthony Ware said in an interview earlier this week.

The FDA said doctors should be alerted to the cancer trends, and some reviewers recommended a “black box” warning about the concerns.

The possibility of a boxed warning, the most serious a drug can bear, took some analysts by surprise, considering the mostly positive tone of the FDA’s review.

“While this is a positive for Lilly shares relative to our bearish stance, it does set the product up for a difficult launch,” Natixis Bleichroeder analyst Jon Lecroy wrote in a note to investors.

The agency plans to ask its outside adviser whether prasugrel’s bleeding side effects could be minimized by restricting use in certain patients.

Lilly seemed to anticipate these concerns in its own documents.

The company suggests not prescribing the drug for patients with a history of stroke or ongoing internal bleeding. Lilly also recomends labeling that would caution doctors about prescribing the drug to patients who are older than 75 or who weigh less than 132 pounds.

Those restrictions would give prasugrel a narrower pool of users than Plavix.

In a separate development Friday, Lilly formally pleaded guilty to a misdemeanor tied to the marketing of its top-seller, the anti-psychotic Zyprexa.

Lilly agreed to the plea earlier this month and will pay about $800 million to resolve a civil case tied to the drug’s marketing. Prosecutors allege Lilly marketed Zyprexa for unapproved uses, including Alzheimer’s-related dementia.

Share of Eli Lilly fell $1.15, or 3 percent, to close at $36.82.