Drugmakers should use more realistic methods for evaluating the effectiveness of birth control pills, patches and other hormonal contraceptives, a U.S. panel of experts said on Tuesday.

Of particular concern is finding out how well such products work for obese women at a time when a growing number of Americans are struggling with their weight, the panel of gynecologists, researchers and other medical experts told the Food and Drug Administration.

Overweight women, smokers and those already at risk for blood clots - a common side of the drugs - are often excluded from company studies on how well such contraceptives work.

“These women, like all women, need contraceptives,” said panelist Dr. Julia Johnson of the University of Vermont.

Panel chairman Dr. Charles Lockwood of Yale University, said the panel agreed “that real world testing is necessary.”

The FDA called on the outside advisers as it takes a closer look at how it evaluates most hormonal contraceptives in light of how they are actually used once approved. It did not seek advice on implanted or injected products.

“The pregnancy rates obtained from clinical trials may be markedly better than the actual pregnancy rates observed when women in the general population use the product, often in a less consistent and reliable manner,” FDA staff said in a summary released before the meeting.

The panel meeting came as a variety of contraceptives are entering the U.S. market.

Makers of birth control pills include Johnson & Johnson, Bayer AG and Barr Pharmaceuticals Inc.. J&J also sells a contraceptive skin patch, while Akzo Nobel NV unit Organon BioSciences markets a contraceptive ring that is inserted into the vagina.

Wyeth is awaiting FDA approval to sell its new Lybrel pill, designed to eliminate monthly bleeding.

“The purpose of this two-day meeting is to discuss clinical trial designs that reflect the diversity of users of hormonal contraceptives, expectations for efficacy and safety, and user acceptability of the newer generation products,” the FDA said in a statement late on Tuesday.

At the meeting, panelists said the FDA should work with the industry to find better ways to include a wider range of women in studies without making it too burdensome for manufacturers.

Still, panelist and Maryland physician Bruce Stadel said it was imperative for companies to “test what they propose to market in the people they’re proposing to market to.”

Likewise, they called on drugmakers to compare new products against other widely-used, recently-approved contraceptives, rather than against use of no contraceptive at all.

Also at issue is the rising pregnancy rate among contraceptives studied in the last decade.

FDA officials have said they have seen higher pregnancy rates in recent trials, but it is unclear whether that is due to lower hormone doses, improper use, or other factors.

Birth control pills approved from 1960 to 1970 saw less than one pregnancy for every 100 women who took them for a year. In the past 10 years, however, some were approved with rates above two per 100 women.

FDA staff have been divided over whether to limit acceptable pregnancy rates with new products. Even so, “the newer generation products are highly effective in preventing pregnancy,” the agency said in its statement.

Panelists said estimating the risk per 100 women, although widely used, was a “crude” way to establish pregnancy risk and manufacturers should move toward a more comprehensive method.

On Wednesday, the panel is expected to discuss contraceptives that prevent bleeding, post-marketing studies and other issues.