Are You a GLP-1 Nonresponder?

GLP-1 medications have changed the weight loss landscape, but as their use expands, some people discover they fall into a less-discussed category: nonresponders.

The term refers to people who do not experience a meaningful benefit from a medication after an adequate dose and duration. In obesity care, “meaningful” has a specific clinical definition: losing at least 5% of starting body weight—a threshold associated with health improvements.

For the GLP-1 medications that have become household names—semaglutide (Wegovy) and tirzepatide (Zepbound)—most participants in clinical trials met that threshold. Still, a consistent minority did not. Across major studies of semaglutide and tirzepatide, roughly 10% to 15% of patients failed to lose at least 5% of their starting body weight. For example, that would mean a loss of less than 10 pounds for a man weighing 200 pounds when he started.

Outside the controlled conditions of clinical trials, outcomes are more variable, shaped by factors including medication tolerance, adherence, and access.

Avlin Imaeda, MD, PhD, a Yale Medicine gastroenterologist who is board-certified in obesity medicine, says part of the problem is that many patients hope to see at least 10% body weight loss, and measure success against that bar.

Most people do achieve significant weight loss, Dr. Imaeda notes, and the true nonresponders—those with less than 5% body weight loss—are rare. “I don’t see that often,” she says. “But that doesn’t mean the medication was a total failure, because we know that even a smaller amount of weight loss can have health benefits.”

If you aren’t getting results on a GLP-1 weight-loss medication, Dr. Imaeda says the first step is to look at your diet.

“Sometimes people haven’t made meaningful dietary changes,” Dr. Imaeda says. “They may still be drinking soda or eating fast food, which can either make them feel sick or limit how well the medication works.”

Certain medical factors, such as thyroid disorders, can disrupt metabolism. She also evaluates blood sugar control, often measured by hemoglobin A1C, which reflects average glucose levels over several months. People with impaired glucose regulation, including those with diabetes, tend to lose less weight on these medications.

It’s also possible that another underlying condition, perhaps a less common one, could play a role. “Sometimes, despite doing everything right, a patient just doesn’t respond the way we’d hope,” she says.

And this isn’t unique to weight-loss medications—some patients may not respond to certain blood-pressure drugs, antidepressants, or cancer therapies. Biology is complex, and treatment responses can vary widely from person to person.

That variability shows up consistently in studies and among patients, says John Morton, MD, MPH, chief of Yale Medicine Bariatric and Minimally Invasive Surgery and a board-certified obesity medicine specialist.

“Across clinical trials, about 10% of patients see little to no weight loss with GLP-1 medication,” Dr. Morton says. “I avoid using terms like failure as it can imply a personal responsibility for weight loss when genetic, treatment-related, or environmental factors may be the cause of non-response,” he says.

In practice, he adds, those patients who don’t respond often have more advanced obesity, with a body mass index (BMI) above 40—a group that has been underrepresented in many GLP‑1 studies, where the average BMI has typically been in the mid‑30s. BMI is a measure of body weight relative to height, commonly used to assess obesity.

If you aren’t losing weight as you’d expected and you’ve tried the highest available doses, it’s worth discussing with your clinician. In such cases, Dr. Imaeda says she might add a different medication to the mix. Options may include phentermine-topiramate, a combination medication that suppresses appetite, as well as medications originally approved for other conditions, such as the antidepressant bupropion (Wellbutrin) or the diabetes drug metformin.

Dr. Imaeda says she often switches patients from Wegovy to Zepbound if possible because Zepbound is more effective in her practice, and in randomized controlled trials. But she is more cautious about moving patients from Zepbound to Wegovy.

“Sometimes, patients want to switch back to Wegovy from Zepbound if they had started with Wegovy and thought they got faster weight loss initially,” Dr. Imaeda says. “I recommend against this because changing reflects perception more than true effectiveness and tirzepatide does work better than semaglutide for most patients.”

Researchers believe genetics may help explain why people respond differently to weight-loss treatments. Genetic factors can influence appetite, feelings of fullness, and how the body uses energy—core processes involved in weight regulation.

But Dr. Imaeda cautions that the genetic effects identified so far appear to be modest.

“Genetics may play a role, but the differences seen in studies don’t fully explain the wide range of responses we see in clinical practice,” she says.

While rare single‑gene conditions can cause severe obesity, Dr. Imaeda says most patients don’t fit into a single genetic category. Instead, clinicians often see patterns in how people experience hunger and fullness—differences that may help explain why GLP‑1 medications feel transformative for some patients.

“Some people tell me they’ve never really felt full before,” she says. “For them, starting a GLP‑1 can be the first time they experience that sensation.”

Yes—at least on average. Dr. Imaeda says women tend to lose more weight on GLP‑1 medications than men. “Men actually tend to respond worse,” she says. “That’s something we see consistently.”

Why that difference exists isn’t fully understood. Some researchers have suggested that hormones such as estrogen may interact with pathways involved in appetite and energy regulation, potentially increasing sensitivity to GLP‑1 drugs. But Dr. Imaeda cautions that this remains a theory.

“We don’t really understand why women respond better,” she says. “It could be hormonal, behavioral, or related to social factors—or some combination of all three.”

In some cases, yes. Dr. Imaeda says she has seen patients lose more weight than intended, particularly on newer medications such as tirzepatide.

“I’ve had patients reach a normal body mass index and then need to reduce their dose,” she says.

When that happens, she explains, the goal isn’t to stop treatment but to adjust it. As people lose weight, they may need less medication to maintain the same effect. “It’s about finding the dose that works for that individual over time,” Dr. Imaeda says.

For patients who don’t respond well to GLP‑1 medications or don’t achieve the weight loss they’re hoping for, other treatment paths exist.

For those who qualify, weight‑loss surgery may be the right choice, Dr. Imaeda says. Procedures such as gastric sleeve or gastric bypass lead to greater average weight loss than medication alone and have demonstrated long-term survival advantage. For some people with higher BMIs, combining surgery with a GLP‑1 medication can be especially effective.

“It’s not for everyone, and not everyone is interested,” she says. “But if someone is eligible, I always want them to understand that it’s an option.”

Looking ahead, Dr. Imaeda says newer and higher‑dose medications that are not yet FDA-approved may be effective for nonresponders.

She acknowledges that for patients who have struggled with weight for years, learning that a medication hasn’t worked can be deeply discouraging.

“It can be a heartbreaking conversation,” she says. “But it doesn’t mean someone has failed—or that there’s nothing left to try.”

Doctors may adjust doses, consider other medications, revisit lifestyle supports, or discuss surgery when appropriate. “The most important thing,” Dr. Imaeda says, “is that we don’t stop the conversation.”