NEW YORK — This could make media owners sick: Pharmaceutical ad spending they count on to exceed $5 billion a year is losing its potency.

Two recent reports say drugmakers cut ad spending in the first six months of this year. TNS Media Intelligence puts the drop at 3.9 percent to $2.4 billion. Rival ad tracker Nielsen Monitor-Plus calculates the decline at 4.8 percent to $2.7 billion.

The reports follow a well-publicized Harvard Medical School study that found consumer ads had little effect on prescription drug sales.

Researchers focused on ads for three drugs: Enbrel (for rheumatoid arthritis), Nasonex (nasal allergies) and Zelnorm (irritable bowel syndrome). Results showed that direct-to-consumer ads "probably aren't as effective as widely perceived," says Michael Law, lead author of the study published in the British Medical Journal last month.

That bodes ill for the magazines, newspapers and radio and TV outlets for which the ads have been a prescription for profits. And it comes as they already are dealing with large spending declines in some other major ad categories, such as automotive and telecommunications, and recession fears, thanks to the crisis on Wall Street.

Magazines and radio stations have seen the most drug ad decline. Second-quarter spending in magazines fell 29 percent to $358 million, according to TNS, while radio plummeted 62 percent to $4 million.

Those declines are an abrupt reversal from the robust spending growth a few years ago.

"Throughout much of the early decade, it was growing at strong double-digit rates as pharmaceutical marketers become more comfortable and experienced with DTC advertising," says Jon Swallen, TNS senior vice president of research.

Among factors driving the drop, he says, are fewer new drug launches, fear of government regulation and cuts by a few brands that had spent big.

Sepracor's Lunesta, an insomnia drug known for its glowing moth icon, spent $75 million on ads in the first quarter of 2008 versus $175 million in that quarter in 2007. Takeda Pharmaceuticals North America's Rozerem sleep aid cut spending from $91 million in the first half of 2007 to $15 million in the first half this year.

Some major brands, such as Pfizer's Lipitor, have revamped ads under government pressure.

"The pharmaceutical companies perceive the threat of government regulation on marketing to be a stronger threat now than it has been in the past," and are trying to self-regulate, says Swallen.

Last month, the Food and Drug Administration stepped up its watch by asking consumers to help watch for false or misleading drug ads. It launched a "Be Smart about Prescription Drug Advertising" area online at FDA.gov. The site encourages consumers to keep an eye out for false or misleading ads and provides a link to report violators.