New U.S.-Canadian research shows that direct-to-consumer (DTC) advertising’s effects on drug sales are unnoticeable.

In 2005, US pharmaceutical companies spent an estimated $3 billion on such ads, but the DTC advertising had only a modest effect on the sales of drugs, US and Canadian researchers said in a research-study released yesterday by British Medical Journal.

Most countries ban direct advertising of prescription medications, with the exceptions of the United States and New Zealand.

Medical ethicists fear that DTC ads may lead to inappropriate prescribing because consumers may ask for drugs they saw advertised in print or on TV.

The new research focused on three drugs: Enbrel, or etancercept, sold by Wyeth and Amgen to treat rheumatoid arthritis and other conditions; Nasonex, prescribed for nasal allergies and Zelnorm, Novartis AG’s now-withdrawn irritable bowel drug.

The researchers looked at whether prescription rates for these drugs increased in English-speaking regions following the launch of U.S. ad campaigns. They used French-speaking Quebecois as their control group. They looked at prescription data from 2,700 pharmacies compiled by IMS Health Canada.

At the end of the study, researchers found no difference in sales for Enbrel or Nasonex after the U.S. ads began. Sales of Zelnorm initially increased in English-speaking regions as soon as the U.S. ad campaign began, but after a few years, sales flattened out.

Drugs are not typical consumer products, Harvard Medical School’s Stephen Soumerai explained. Advertising prescription drugs is “not like popcorn, cereal and hair sprays,” he said, adding that decisions to market directly to consumers are based on scant data.