But the extra prescriptions were limited to women with a medical reason for taking those drugs. The ads didn't seem to increase the inappropriate use of aromatase inhibitors, which include letrozole (marketed as Femara) and anastrozole (Arimidex).

That's in contrast to some previous studies that found so-called direct-to-consumer (DTC) advertising of antidepressants, for example, led to increases in prescriptions both for patients who needed them and those who didn't.

"We know it increases demand for prescription drugs," said Julie Donohue, a health policy researcher at the University of Pittsburgh who has studied direct-to-consumer advertising.

"What we don't have a handle on is whether it's stimulating primarily appropriate use or inappropriate use. Probably some combination, but we don't know the ratio at all."

Besides the United States, the only country that allows direct-to-consumer advertising is New Zealand, according to the World Health Organization. Top drugs marketed to patients include sleep aids and medications to treat high cholesterol.

Aromatase inhibitors are prescribed to older women who have had breast cancer to prevent it from coming back. Because they work by blocking the body from producing estrogen, the drugs aren't supposed to be used in pre-menopausal women.

Tamoxifen is the drug of choice in younger women with hormone receptor positive breast cancer - the most common type - and an alternative to aromatase inhibitors in older women.

For the new study, researchers led by Dr. Gregory Abel from the Dana-Farber Cancer Institute in Boston compared drug companies' monthly U.S. spending on direct-to-consumer ads for aromatase inhibitors with nationwide pharmacy data on the number of prescriptions for those drugs.

Between 2005 and 2007, spending on ads varied widely - from just over $22 million in October 2005 to less than $120,000 in January 2007.

Every million dollars spent over a month was tied to a 0.15-percent increase in aromatase inhibitor prescriptions three months later, the researchers reported in the journal Cancer.

However, when they looked specifically at older - likely post-menopausal - women and much younger women, ad spending was linked primarily to a rise in prescriptions for the older women.

A 0.18-percent increase in prescriptions for women over 60 accompanied every million ad dollars spent, but there was no increase among those 40 and younger.

Donohue, who wasn't involved in the new study, said that in the case of aromatase inhibitors, it's relatively easy for doctors to decide when it's OK to prescribe the drugs, and for researchers to look back at patient records and figure out when the drugs were prescribed appropriately.

"It gets really tricky with something like depression," she told Reuters Health - when the lines between minor and major depression can be blurry.

She said what doctors prescribe is often influenced by patient requests, with antibiotics being a prime example.

Donohue also pointed out that drug marketers not only print ads for doctors just as they do for potential patients, but they also send company representatives bearing free samples to visit doctors. That could also impact what doctors prescribe - and it's not clear whether that was a factor in sales increases of aromatase inhibitors.

"While it is the most visible form of promotion, DTC is actually a smaller part of the marketing budget than advertising and other forms of promotion to physicians," Donohue said.

"We can't really know from this particular study which part of the equation was responsible for there not being inappropriate use. Was it that patients appropriately classified themselves and the women under 40 didn't go to their doctors and ask (for aromatase inhibitors), or did doctors do the right thing for women under 40 and say ‘no?'"

SOURCE: bit.ly/TO4lSl Cancer, online November 6, 2012.

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