Watchdog group Public Citizen urged U.S. regulators to withdraw approval of Novo Nordisk's diabetes drug Victoza, saying it increases the risk of serious health problems like thyroid cancer and kidney failure.

Public Citizen said the drug was approved in 2010 against the advice of three reviewers from the U.S. Food and Drug Administration, according a petition filed to the FDA on Thursday.

"The (approval) was a huge blow to the health and safety of diabetics in this country," said Dr. Sidney Wolfe, director of Public Citizen's Health Research Group, in an interview. Wolfe also serves as the consumer representative on the FDA's advisory panel for drug safety and risk management.

Public Citizen, a nonprofit consumer advocacy group, is a frequent critic of industry. Its past petitions have sometimes prompted action or hearings from the FDA, though a response could take years.

The FDA said it will review the petition and respond directly to Public Citizen.

Denmark-based Novo said the FDA reviewed data from almost 4,000 patients before deciding to approve Victoza, and that doctors and patients should be confident in the drug's safety.

"Novo Nordisk is committed to patient safety and rejects Public Citizen's assertion that the benefits of Victoza are outweighed by its risks," the company said in a statement.

Victoza, known generically as liraglutide, treats adults with type 2 diabetes. It is one of Novo's biggest sellers, with global sales of 2.1 billion Danish crowns ($370 million) in the fourth quarter of 2011.

About 150,000 prescriptions for the drug are filled each month in the United States, Public Citizen said, citing data from IMS Health.

Novo Nordisk is also hoping to gain U.S. approval for Victoza as an obesity treatment by 2014, the company has said.

An advisory panel to the FDA in 2009 raised questions about the medication's safety, but the FDA ultimately decided the drug's benefits in controlling blood sugar outweighed its risks.

In clinical trials, pancreatitis, or inflammation of the pancreas, occurred more often with Victoza than with other diabetes drugs.

High doses of the drug also caused thyroid tumors in rats and mice, although the FDA said at the time that it was not known if Victoza would also cause thyroid cancer in people.

As a condition of approval, the FDA asked Novo Nordisk to conduct a five-year study to look at Victoza's risk of pancreatitis, seriously low blood sugar levels, allergic reactions, and thyroid and other cancers. The FDA also asked the company to test the drug's heart safety.

A director inside the FDA's office of new drugs, Dr. Curtis Rosebraugh, overruled some other FDA staff, including the clinical safety reviewer, in approving the drug, according to documents posted on the FDA's website.

"It should not be surprising that in an application of this complexity there are a variety of opinions internally as to what the appropriate course of action should be," he wrote.

Dr. Karen Mahoney, the safety reviewer, said at the time that there were already 11 types of drugs approved for type 2 diabetes, so there was less urgency to approve a new drug with uncertain safety.

But Dr. Rosebraugh said some safety issues could be addressed in studies once the drug is approved, and Victoza was not any more risky than other drugs in the same class, such as exenatide, the generic name for Amylin Pharmaceuticals's Byetta.

"I am not willing to keep such medications from patients for years while we await the results of mechanistic studies that may not even actually answer the question of human relevancy," he wrote in a summary explaining his decision.

He said he favored approval of Victoza as a second-line drug, meaning it should only be prescribed if people had failed to treat their diabetes with another drug.

In the first 17 months after the drug reached the U.S. market, 200 people who took it got acute pancreatitis, according to Public Citizen's analysis of the FDA's database of complaints. The number could be even higher since most people do not report problems to the FDA, the group said.

The FDA also later amended the label for Victoza to include the risk of kidney failure.

Public Citizen's Wolfe said describing serious safety issues on drug labels is "reckless" since it has not deterred doctors and patients from taking the drug.

"Clearly, the FDA's warning system is not sufficient," Wolfe said. "The drug should be taken off the market."