Weight-loss medications have come a long way — from the amphetamine-based “rainbow pills” of the 1950s and ’60s to the infamous Dexatrim of the ’80s and the fen‑phen era of the ’90s. Not only were many of these treatments controversial, but they also came with significant safety concerns.

Today, glucagon-like peptide-1 medications (GLP-1s) represent a newer class of weight-loss treatments and a fundamentally different approach compared to the stimulant-based pills of the past. They work by mimicking a natural gut hormone that helps regulate blood sugar and reduce appetite by acting on hunger signals in the brain.

GLP-1 medications have quickly become one of the most widely used weight-loss therapies. In the U.S. alone, an estimated 1 in 8 adults — nearly 12% of the population — have reported using medications such as Wegovy (semaglutide) and Zepbound (tirzepatide).

In clinical trials, these medications have produced significant results. Patients taking semaglutide and tirzepatide lost about 15% to 21% of their body weight on average over time, but those results don’t apply to everyone.

In those same studies, a subset of patients — around 10% to 15% — lost less than 5% of their body weight, the threshold often used to define meaningful weight loss. For those patients, the experience can look very different. Their weight loss may slow, plateau or fail to materialize altogether, even with consistent use.

That’s often when the question “What’s wrong?” starts to surface, but the answer isn’t as clear-cut as you may think.

Why a GLP-1 may not be ‘working’ as it should

“When someone says their GLP‑1 is not working, that can mean a lot of different things," says Dr. Vadim Sherman, medical director of bariatric and metabolic surgery and obesity medicine specialist. "We have to determine whether they’ve hit a plateau, whether they’re a non-responder or whether the medication is no longer having the same effect.”

Plateau

For many patients, weight loss on these medications tends to be greatest early in treatment and then gradually slows over time. This pattern is common in clinical trials of GLP‑1–based therapies, where weight loss progresses most rapidly at the start before leveling off. Eventually, some patients may experience a plateau or a halting of weight loss altogether.

“When you’re losing weight consistently, maybe one to two pounds a week, and then you go a month without losing anything, that is considered a plateau,” Dr. Sherman explains.

In many cases, that doesn’t mean the medication has stopped working. GLP‑1 medications still help regulate appetite, but the rate of weight loss often slows as the body adapts and the initial response levels off, which can lead to a plateau.

(Related: 5 Ways to Break a Weight Loss Plateau That Actually Work)

Non-response

Then there are patients who may not experience any meaningful weight loss despite consistent use. These are what clinicians refer to as non-responders.

“There’s a pretty high percentage of people that when you give them these medications, they just really have no effect from them — no real change in appetite and no meaningful weight loss,” he says.

GLP‑1 therapies primarily target hunger and appetite, but those aren’t the only factors that influence weight. In these cases, the factors driving a patient’s weight may not respond strongly to this type of treatment.

Not all non-response looks the same, though. Some patients may experience little to no change in appetite or hunger signals, while others may notice some effect but still fall short of meaningful weight loss. That variation is one reason doctors take a closer look before determining what comes next.

Tolerance

In other instances, the medication may have worked — at least initially — but it doesn’t seem to be working as well anymore.

“It’s possible the medication was working before, but over time what we call tolerance can develop, and it may no longer have the same effect,” Dr. Sherman says.

In many cases, this doesn’t reflect true “tolerance” in the traditional sense. Instead, it may be part of a natural shift in how the body responds to ongoing weight loss. As weight decreases and the body adapts, the overall effect on weight can become less pronounced, even if appetite remains controlled.

Regardless of the mechanism, the outcome can feel similar: progress slows or stops. But clinically, that doesn’t necessarily mean the medication has stopped working.

Misaligned expectations

In other instances, the issue isn’t how well the medication is working, but how the results are being interpreted.

“The first thing we have to understand is what the patient’s expectations are for weight loss and what these medications can realistically provide,” Dr. Sherman says. “Patients often have a personal goal they want to meet, but the medication may not be enough to reach that goal.”

Patients often approach treatment with a specific goal in mind — a target weight or a certain rate of loss — that may not align with what the medication is able to deliver on its own.

When expectations and outcomes don’t align, it can feel like the treatment isn’t working, even when it may be having a meaningful effect. In those cases, the focus often shifts to adjusting expectations or adapting the overall approach to better match the patient’s goals.

(Related: PODCAST: Factors That Affect Weight Loss Beyond Diet & Exercise)

There are limits to what GLP‑1 medications can do

While GLP‑1 medications can have a powerful effect on appetite, they don’t control every factor that influences weight.

“A GLP‑1 doesn’t directly cause weight loss — it affects hunger and appetite. When you use that together with dietary and lifestyle changes, that’s when you get weight loss.”

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Dr. Vadim Sherman, medical director of bariatric and metabolic surgery and obesity medicine specialist

In other words, the medication plays one role in a much larger system. It can help reduce hunger and make it easier to eat less, but it doesn’t override the many biological and behavioral factors that contribute to weight over time.

Those factors can include metabolism, hormone signaling, how the body processes and stores energy and even how full someone feels after eating. While GLP‑1 medications are designed to act on appetite and satiety, they don’t address all of the systems involved in weight regulation.

That’s part of what distinguishes different medications within this category. Semaglutide works by mimicking a single hormone involved in appetite regulation, GLP-1. Tirzepatide builds on that by targeting two pathways, including GLP‑1 and glucose-dependent insulinotropic polypeptide (GIP) — which can enhance its effect for some patients. And newer therapies currently in development, such as retatrutide, aim to target three different hormone pathways at once.

Even so, these medications are still only influencing part of a much more complex system, which is why responses can vary from one person to another.

“At some point, the medication may have done all that it’s going to do,” he adds. “There are biological limits to what any one therapy can accomplish.”

Instead, it may reflect the limit of what this type of treatment can achieve for a given patient.

“You have to see how that specific patient’s biology responds to the medication,” Dr. Sherman says. “For some people, the effect is meaningful. For others, it may be more limited.”

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What doctors look at when progress stalls

The first question clinicians like Dr. Sherman will often ask is whether the medication is still having its intended effect on hunger and appetite or if it’s producing the amount of weight loss expected, he says.

“You have to step back and figure out what’s actually limiting progress,” Dr. Sherman says. “We look at whether everything else is optimized, including diet and activity.”

GLP‑1 medications can help reduce hunger, but weight loss still depends on how that effect translates into day‑to‑day habits, including what and how much a patient is eating, as well as overall activity levels.

Doctors may also consider how a patient’s response has changed over time. If weight loss slows after an initial period of progress, it may indicate a plateau or a shift in how the body is responding to the medication.

“If we’re not seeing the results we’re hoping for, we have to think about what else might be effective for that patient,” Dr. Sherman says.

In some cases, adjusting the medication may be enough. Increasing the dose, switching to a different medication or combining approaches can sometimes lead to additional progress. In others, the response may remain limited despite those changes.

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At that point, the conversation often shifts.

“If a patient doesn’t respond very well to weight loss medications, continuing to take them may not make sense,” Dr. Sherman says. “Continuing to increase the dose or incur that expense can be counterproductive.”

Without insurance coverage, these medications can cost more than $1,000 per month, which can make long-term use difficult to justify for some patients — especially if results are limited.

“That’s when we start to explore other options for weight loss,” he adds. “There’s a point where you have to move beyond what that medication can do.”

When medications alone aren’t enough for weight loss

For some patients, moving beyond medication means considering a different type of treatment altogether. The goal at that point is to find an approach that better matches the factors driving your weight and supports more meaningful, sustained progress.

Bariatric surgery is one option doctors may discuss when progress with medication is limited or when a more significant, sustained result is needed. The term refers to a group of procedures — most commonly gastric sleeve and gastric bypass surgeries — that fundamentally alter how the digestive system works.

Because of these changes, bariatric surgery often leads to different outcomes, including weight loss of about 25% to 30% or more of total body weight, with long-term data showing more sustained results for many patients.

That doesn’t make surgery the right choice for everyone, though.

“We approach weight loss as a spectrum of treatment options,” Dr. Sherman says. “The goal is to find the approach that best matches the patient and what’s driving their weight.”

For some patients, medication may be enough to reach and maintain their goals. For others, it may be one step in a broader treatment plan. In certain cases — particularly when response is limited or short-lived — surgery may offer a more effective path forward.

“There are many different paths that can lead to the same goal,” Dr. Sherman says. “It’s not a situation where you max out medications and then consider surgery — it’s tailored to the patient.”