he 50 most-advertised prescription medicines contributed significantly last year to the increase in the nation's spending on drugs, according to a study.

The report was prepared by the National Institute for Health Care Management, a nonprofit research foundation that was founded by the Blue Cross Blue Shield health insurance plans.

Increases in the sales of the 50 drugs that were most heavily advertised to consumers accounted for almost half the $20.8 billion increase in drug spending last year, according to the study. The remainder of the spending increase came from 9,850 prescription medicines that companies did not advertise or advertised very little.

The study attributed the spending increase to a boost in the number of prescriptions for the 50 drugs, and not from a rise in their price.

Only the United States and New Zealand permit advertising of prescription medicines to consumers. The advertising has grown more controversial as both the number of ads and spending on prescription drugs continue to rise.

The Food and Drug Administration is now reviewing whether it should change rules it enacted in 1997 that made it easier for pharmaceutical companies to advertise their products on television.

The researchers said that their study did not prove that the growing amount of advertising by pharmaceutical companies was directly causing spending on drugs to rise. Instead, they said, the study only adds to a growing amount of circumstantial evidence that advertising may be part of the reason for the escalating spending.

Among the other reasons for increased spending, the study said, are an aging population, newer drugs that are more expensive than older medicines and an increased use of drugs for chronic conditions like asthma or heart disease that involve taking medicines over long periods.

The big drug companies, however, objected to the study yesterday. The companies said that their research showed no direct link between advertising and rising drug expenses.

The drug companies also said that the researchers had left out the benefits that patients receive from the advertising. The ads encourage patients to consult their doctors about undiagnosed medical problems, the drug companies said.

"We have an epidemic of undertreatment of serious illnesses in the United States," said Alan F. Holmer, the president of the Pharmaceutical Research and Manufacturers of America, the industry's Washington trade group. "Surveys of both patients and physicians show that direct-to-consumer advertising leads patients who would otherwise go without medical care for these terrible illnesses to seek treatment for the first time."

There is also evidence that the ads help remind patients to keep taking the medicines their doctors prescribe, Mr. Holmer said.

But it is also clear that drug companies have increased their advertising spending with the goal of expanding their sales.

According to the study, Vioxx, an arthritis drug sold by Merck & Company (news/quote), was the most-heavily advertised prescription drug and also accounted for more of last year's increased drug spending than any other single drug.

Merck spent $160.8 million to promote Vioxx to consumers — more than PepsiCo (news/quote) spent to advertise Pepsi or Budweiser spent to advertise its beer, the study said. With the help of the advertising, Vioxx sales quadrupled to $1.5 billion last year from about $330 million in 1999.

"About 86 million Americans suffer from pain," said Greg Reaves, a spokesman for Merck. "Our ads encourage patients to speak to their doctors and find out whether Vioxx is right for them."

Celebrex, another arthritis drug, which is locked in a marketing battle with Vioxx, was the seventh most widely promoted drug to consumers and was the fourth-largest contributor to drug sales growth last year.

Other heavily advertised drugs contributing to the rise in drug sales are the cholesterol-lowering drugs, Lipitor, Zocor and Pravachol; as well as Paxil and Prozac, for depression; Claritin, Allegra and Zyrtec for allergies; and Prilosec for ulcers.

Over all, consumer drug advertising rose 35 percent last year, to $2.5 billion from $1.8 billion in 1999, according to the study. Two of the biggest drug companies, Merck and Pfizer (news/quote), increased their advertising much more than the industry average. Merck's total spending on consumer advertising increased 118 percent, the study said, while Pfizer's spending almost doubled.

GlaxoSmithKline (news/quote), the British drug company, spent more on consumer advertising than any other company. It spent $417 million on advertising last year — an increase of 40 percent.

In the last year, the drug advertising has been criticized by doctors, federal legislators and consumer groups.

The American Medical Association, for instance, approved a resolution this summer asking the drug companies voluntarily to place disclaimers on each ad that would state, "Your physician may recommend other appropriate treatments."