More than 40% of American adults are considered obese, yet the medications many take are rarely tested in bigger bodies.
That's because they are not required to be included in drug studies. And often, they're explicitly excluded.
“Clinical trials and dosing instructions don’t always ensure that drugs will be safe and effective for people with obesity,” said Christina Chow, a drug researcher who's reported on the challenges of considering obesity in drug development. “There’s no real emphasis for them to be studied at all.”
Many widely prescribed drugs and over-the-counter medications work differently in people who are obese, but exactly how and at what dose often isn't clear. Research suggests that may include antibiotics and antifungal drugs used to treat serious infections, synthetic hormones used in Plan B emergency contraception and even ibuprofen, the common painkiller sold as Advil.
These states have the highest obesity rates in the US
Obesity rates continue to increase across the U.S., which the CDC says is leading to higher health care costs.
The U.S. Food and Drug Administration and the National Institutes of Health — agencies that regulate and fund drug testing — are putting new focus on the gaps in research. At a workshop last year, FDA Commissioner Dr. Robert Califf acknowledged a "deficit of evidence” about how medicines act in patients who are obese. The NIH now encourages researchers to consider the impact of excluding obese people in their studies, a spokesperson said.
At a recent medical conference, Chow presented a review of more than 200 studies for new drugs in the U.S. last year. Of those, nearly two-thirds failed to mention weight or body mass index — a common assessment of obesity — meaning they wouldn't ensure inclusion of people with obesity, she said.
The studies that did cite weight were most often used to exclude people with obesity from participating, said Chow, who works for Emerald Lake Safety, a California company that investigates severe drug reactions. People with a body mass index or BMI of 30 or higher are considered obese.
From 1999-2020, obesity-related cardiovascular disease deaths tripled
Black individuals, and especially Black women, had higher mortality rates than any other group in the study.
Historically, certain populations have been left out of testing for fear of harm, including pregnant people and children. Women, racial and ethnic minorities and the elderly, too, have been underrepresented before recent efforts to bolster diversity.
The reasons for excluding people with obesity are longstanding and varied, said Dr. Caroline Apovian, a researcher at Brigham and Women’s Hospital in Boston and co-author of Chow's study.
Participants willing to sign up for studies are often leaner and don't reflect the general population, she noted. And researchers often worry that health complications that can come with obesity will cloud the results of their work.
“Sometimes patients with obesity have many more comorbidities than others. They’ll have more diabetes, more heart disease, more strokes,” she said.
But if drugs aren’t studied in a condition that affects 42% of the U.S. population, the real-world consequences can be dire, experts said.
Some drugs can become concentrated in fat tissues and not in the bloodstream. That means there will be less medication in the blood, leading to undertreatment, Apovian said.
Other drugs remain in the body longer in the obese. That could result in harmful drug interactions if another medication is added too soon.
In the meantime, Apovian said patients can ask their doctors about whether the standard dose of a medication is appropriate for their weight. The doctors may not know, but it could start an important conversation about effective treatment.
