BOSTON (Reuters) – Ten years after a rule change allowed drug companies to advertise directly to U.S. consumers, the overall amount spent promoting medicines is 2.6 times what it was in 1996, researchers said on Wednesday.

But direct-to-consumer advertising, which increased by 330% during that period, still only makes up 14% of the nearly $30 billion the companies spend to promote their drugs, according to a study in the New England Journal of Medicine.

The researchers also found evidence that regulators are doing less to police such ads.

Total spending on pharmaceutical promotion grew to $29.9 billion in 2005 from $11.4 billion in 1996, an average annual growth rate of 10.6%, they said.

The "Ask your doctor about" commercials, which sometimes do not even say what a drug is for, have been widely derided and cited as one reason health care costs are rising faster than general inflation.

And while ad campaigns make brand names familiar to consumers, they may also spark cynicism over drug safety when heavily marketed brands come under fire for safety reasons, experts say.

New Zealand also permits such advertising and existing bans in Canada and the European Union are being challenged.

For the study, Julie Donohue of the University of Pittsburgh Graduate School of Public Health and her colleagues looked at industry data from three market-research firms that track advertising spending by the pharmaceutical industry.

"We also obtained information from researchers and staff members at the FDA (U.S. Food and Drug Administration) and other government agencies," they wrote.

The group found that the FDA has been sending out fewer letters to drug companies warning them that their commercials are minimizing risks or exaggerating effectiveness.

In 1997, 142 such letters were sent. Last year there were only 21.

The reason is not clear, but the Donohue team said there is evidence that the government is being lax in its oversight.

"In 2004, four (FDA) staffers were reviewing such advertisements, even though spending on this form of advertising (and probably the volume of ads to review) had increased by 45%, from $2.9 billion to $4.2 billion," the researchers said.

Furthermore, while 64% of the ads broadcast on television in 1999 were reviewed by the FDA, the ratio had declined to 32% by 2004.

In addition, in 2002, when then-Secretary of Health and Human Services Tommy Thompson began requiring all warning letters to be reviewed by the FDA’s Office of Chief Counsel, the number of letters actually sent to manufacturers dropped by half, the researchers said.

A report from the Government Accountability Office concluded that FDA warning letters often were not sent out until false or misleading ad campaigns had run their course.