Sharks may help improve climate forecasts, study finds

Research demonstrates how animal-borne sensors can work in tandem with traditional tools to improve ocean predictions

University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science

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Neil Hammerschlag, Ph.D. and Laura McDonnell, Ph.D. attach a satellite tag to a blue shark that transmitted location, temperature, and depth data. 

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Credit: Nola Schoder, MPS

MIAMI— A new study published in the journal npj Climate and Atmospheric Science, shows that electronically tagged sharks can serve as mobile sensors, collecting ocean climate data in regions that are difficult to observe using conventional methods.

The study is led by Laura H. McDonnell, Ph.D., who conducted the research as a doctoral student at the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science and the Abess Center for Ecosystem Science and Policy. Its findings demonstrate that temperature and depth data gathered by tagged sharks can enhance ocean forecast accuracy in dynamic regions of the Northwest Atlantic.

By incorporating shark-collected data into a seasonal climate model, McDonnell and her team found that forecast errors at the ocean surface decreased substantially in certain regions, with improvements reaching as much as 40 percent in specific cases.

This is the first study to experimentally integrate animal-borne sensor data into a seasonal climate model and quantify its impact on forecast performance, suggesting potential for future operational use.

“Sharks are already moving through parts of the ocean that are challenging for us to observe,” said McDonnell, now a postdoctoral investigator at the Woods Hole Oceanographic Institution (WHOI). “This research shows that data they collect can help fill important gaps and, when used carefully, can improve how we predict ocean conditions.”

Interdisciplinary collaboration fuels innovation

The study originated from an interdisciplinary collaboration between former Rosenstiel School shark scientist Neil Hammerschlag, Ph.D. and atmospheric scientist Ben Kirtman, Ph.D., now dean of the Rosenstiel School. In 2018, they recognized that the data from shark-tagging studies used by Hammerschlag’s lab to study shark ecology could also benefit climate modeling.

Satellite tags attached to sharks record depth and temperature as they travel through the ocean, collecting and transmitting this data in near real time. While these tags have long helped scientists track shark movements, the collaboration opened a new application and a chance to create a novel proof of concept: using the same data to improve climate forecasts.

“Marine predators like sharks naturally seek out dynamic ocean features such as fronts and eddies,” said Kirtman. “These are areas where models often lack sufficient observations.”

Supported by a grant from Cisco Systems, the team conducted fieldwork and tested the concept.

Testing sharks as ocean observers

McDonnell and Hammerschlag tagged 18 blue sharks (Prionace glauca) and one shortfin mako shark (Isurus oxyrinchus) in the Northwest Atlantic. The sharks transmitted more than 8,200 temperature-depth profiles across a wide range of locations and depths—down to nearly 2,000 meters. WHOI oceanographer and study co-author Camrin Braun, Ph.D., helped facilitate this field work off Cape Cod, MA by connecting McDonnell and Hammerschlag with a local fisherman and co-led the forecast data analysis.

“Key to this study was repurposing a more advanced tag capable of transmitting location data along with temperature and depth information,” said Hammerschlag, co-author of the study and executive director of the Shark Research Foundation. “This allowed us to link subsurface ocean conditions directly to specific locations with known accuracy.”

Kirtman integrated a subset of these data into the Community Climate System Model, a coupled ocean–atmosphere–ice–land model used in seasonal forecasting applications that forms part of the National Oceanic and Atmospheric Administration’s operational North American Multi-Model Ensemble (NMME) system, of which Kirtman is the lead scientist.

The team compared the actual resulting climate conditions with the forecasted predictions from traditional models as well as the ones that integrated the shark collected data.

The results showed measurable improvements in forecast performance, particularly in dynamic coastal and shelf regions that are important for marine ecosystems and fisheries.

The researchers emphasize that animal-borne sensors are not a replacement for traditional observing systems but a complementary tool.

“Tagged sharks won’t replace conventional observing systems,” added McDonnell. “What the preliminary results do show is that tagged marine predators can provide complementary in-situ observations at the surface and at depth.”

Why it matters

Accurate ocean forecasts are critical for fisheries management, marine operations, and understanding how climate variability affects coastal communities. However, forecasts are often least reliable in regions where conditions change rapidly and observational data are lacking.

Animal-borne sensors could enhance predictions that support decision-making across multiple sectors, ranging from seafood supply chains to climate adaptation planning.

“Marine animals are already being tracked to understand their behavior in relation to environmental conditions, but this study reveals how these data can also be leveraged for forecasting and climate applications,” said Hammerschlag.

“For fisheries and coastal communities, small improvements in ocean forecasts can make a big difference,” said Braun. “Reducing uncertainty helps people plan, whether that’s where to fish, how to manage resources, or how to respond to changing conditions.”

The study, titled “Improved seasonal climate forecasting using shark-borne sensor data in a dynamic ocean,” was published on April 28, 2026 in the journal npj Climate and Atmospheric Science.

Funding for the research was provided by Cisco Systems (AWP-014524) and the University of Miami Abess Center.

The authors and their affiliations for this study are as follows: Laura H. McDonnell & Neil Hammerschlag, Rosenstiel School of Marine, Atmospheric and Earth Science, and the Leonard and Jayne Abess Center for Ecosystem Science and Policy at the University of Miami. Ben P. Kirtman, Rosenstiel School and the Cooperative Institute for Marine and Atmospheric Studies, and the Frost Institute for Data Science and Computing, all at the University of Miami, and Camrin D. Braun, Woods Hole Oceanographic Institution.

About the University of Miami and Rosenstiel School of Marine, Atmospheric and Earth Science

The University of Miami is a private research university and academic health system with a distinct geographic capacity to connect institutions, individuals, and ideas across the hemisphere and around the world. The University’s vibrant academic community comprises 12 schools and colleges serving more than 19,000 undergraduate and graduate students in more than 180 majors and programs. Located within one of the most dynamic and multicultural cities in the world, the University is building new bridges across geographic, cultural, and intellectual borders, bringing a passion for scholarly excellence, a spirit of innovation, and a commitment to tackling the challenges facing our world. The University of Miami is a member of the prestigious Association of American Universities (AAU).

 Founded in 1943, the Rosenstiel School of Marine, Atmospheric, and Earth Science is one of the world’s premier research institutions in the continental United States. The School’s basic and applied research programs seek to improve understanding and prediction of Earth’s geological, oceanic, and atmospheric systems by focusing on four key pillars:

*Saving lives through better forecasting of extreme weather and seismic events. 

*Feeding the world by developing sustainable wild fisheries and aquaculture programs. 

*Unlocking ocean secrets through research on climate, weather, energy and medicine. 

*Preserving marine species, including endangered sharks and other fish, as well as protecting and restoring threatened coral reefs. www.earth.miami.edu

Sharks may help improve climate forecasts, study finds [VIDEO] 

 

Example shark-derived temperature–depth profiles across four regions, with the distribution of all transmitted profile locations (October 2021–April 2022). Top panels compare tag-derived profiles within a 1° × 1° grid cell on a given day to the concurrent control (CFSR) profile (black), with shark tag data showing minimum (blue) and maximum (red) temperatures. Summary statistics for each grid cell are provided in-panel. The bottom map shows all profile locations and maximum depths (N = 8,242), with colored diamonds marking example profiles, orange lines indicating the Gulf Stream, and the black line marking 200 m depth.

Credit

Laura McDonnell, Ph.D.

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Journal

npj Climate and Atmospheric Science

DOI

10.1038/s41612-026-01394-9 

Method of Research

Experimental study

Subject of Research

Animals

Article Title

Improved seasonal climate forecasting using shark-borne sensor data in a dynamic ocean

 

Cannabis microdosing more common than psychedelics among US adults, national survey finds

Across substances, people reporting poorer mental health were more likely to report microdosing

University of California - San Diego

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Key takeaways:

• Cannabis is the most commonly microdosed substance in the U.S., with about 9.4% of adults — roughly 24 million people — reporting lifetime use. More people reported microdosing for recreational reasons than for medical reasons.

• Cannabis microdosing was nearly twice as common as psilocybin, LSD or MDMA, challenging the perception that microdosing is mainly a psychedelic practice.

• Microdosing was more common among people reporting poorer mental health.

Researchers from University of California San Diego have found that microdosing — taking very small amounts of psychoactive substances — is more common among U.S. adults than previously recognized, with cannabis leading by a wide margin. The study, published May 4, 2026 in the American Journal of Preventive Medicine, estimates that millions of Americans have microdosed substances such as cannabis, psilocybin, LSD (“acid”) and MDMA (“ecstasy”).

“Microdosing is often discussed in the context of psychedelics like psilocybin or LSD, but what surprised us most was that cannabis microdosing was almost twice as common,” said Kevin Yang, MD, resident physician in the Department of Psychiatry at UC San Diego School of Medicine and first author of the study. “That suggests conversations about microdosing may be overlooking a large group of people who are using small amounts of cannabis in similar ways.”

“Most proponents of microdosing recommend use under specific protocols that involve taking low doses of LSD or psilocybin for specific health applications,” said Eric Leas, PhD, MPH, assistant professor at the UC San Diego Herbert Wertheim School of Public Health and Human Longevity Science and senior author of the study. “That’s not what we found. Most people are microdosing for recreational purposes. That suggests that many people could think about the concept of ‘microdosing’ more as a way of lowering dosage. They may just want to take less, so they don’t want to get as high.”

Microdosing typically involves consuming about one-fifth to one-twentieth of a typical recreational dose, with the goal of avoiding strong psychoactive effects while potentially experiencing subtler benefits such as improved mood, reduced anxiety or enhanced creativity.

To better understand how common the practice is, researchers analyzed data from a nationally representative survey of 1,525 U.S. adults conducted in late 2023 through the Ipsos KnowledgePanel, which uses probability-based sampling to reflect the U.S. population. Participants were asked whether they had ever intentionally microdosed cannabis, psilocybin mushrooms, LSD or MDMA.

The results suggest that cannabis is the most commonly microdosed substance. About 9.4% of U.S. adults — an estimated 24.1 million people — reported microdosing cannabis at least once in their lifetime. In comparison, 5.3% reported microdosing psilocybin, 4.8% LSD and 2.2% MDMA.

Ongoing microdosing was less common but still measurable: roughly 3.3% of adults reported currently microdosing cannabis, compared with about 1.0% for psilocybin, 0.6% for LSD and 0.3% for MDMA.

The study also found that the reasons for microdosing differed by substance. Cannabis microdosing was most often reported for medical reasons, including managing anxiety, depression or chronic pain. In contrast, psilocybin, LSD and MDMA were more frequently microdosed for recreational purposes, such as achieving a milder psychoactive experience.

Researchers also observed patterns tied to mental health and policy environments. Across substances, people reporting poorer mental health were more likely to report microdosing. For example, cannabis microdosing was reported by about 21% of adults who rated their mental health as “poor,” compared with about 8% among those reporting “excellent” mental health.

In addition, microdosing of psychedelics such as psilocybin and LSD was more common in places where laws were more permissive — meaning, jurisdictions that have decriminalized psychedelic possession. The findings suggest that changes in drug policy may influence both access to these substances and people’s willingness to report using them.

Despite growing public interest, the researchers emphasize that scientific evidence on the health effects of microdosing remains limited. Few placebo-controlled clinical trials have been conducted and existing studies have produced mixed findings about potential benefits. Additional risks stem from the unregulated nature of many of these substances, including the possibility of adulterated products or dosing errors — especially since most people who microdose do not test the substances they use.

“There’s a lot of anecdotal enthusiasm around microdosing, especially for mental health,” said Leas. “But we still need rigorous studies to determine whether these perceived benefits are real, who might benefit and what the potential risks could be.”

The authors note that because the study was cross-sectional, it cannot determine whether microdosing influences mental health outcomes or whether people experiencing mental health challenges are more likely to try microdosing. Future research, including longitudinal studies and clinical trials, will be needed to clarify those relationships.

As cannabis legalization and psychedelic policy reforms continue to evolve across the United States, the researchers say monitoring patterns of microdosing will become increasingly important for public health.

“Microdosing appears to be a growing behavior that cuts across different substances and motivations,” Leas said. “Understanding how and why people are using these small doses is essential if we want to develop evidence-based policies and guidance for clinicians and the public.”

Link to full study: https://doi.org/10.1016/j.amepre.2026.108381

Additional co-authors on the study include: Joseph Friedman, MD, and Siyuan Ping from UC San Diego. Nora Satybaldiyeva, PhD, and Wayne Kepner, PhD, from Stanford University.

The study was funded, in part, by the U.S. National Institute on Drug Abuse (grant #K01DA054303, PI: Leas). Satybaldiyeva acknowledges salary support from the National Heart, Lung, and Blood Institute (grant #5T32HL161270-03). Kepner acknowledges salary support from the National Institute on Drug Abuse of the National Institutes of Health (#T32DA035165), and the William and Katharine Duhamel Addiction Medicine Fund.

Authors declare no competing interests.

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Journal

American Journal of Preventive Medicine

DOI

10.1016/j.amepre.2026.108381 

 

How do rats determine whether to approach or avoid distressed peers?

Researchers identified a pathway in the rat brain that plays a role in evaluating social signals and making decisions to approach stressed pups or avoid stressed adult peers.

Society for Neuroscience

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In a new JNeurosci paper, a Boston College research team led by John Christianson explored how a pathway between two areas of the brain—the insular cortex and prefrontal cortex—supports social decisions in male rats. Why did the researchers choose to assess the insular cortex and prefrontal cortex of rats? Says Christianson, “For rodents and humans alike, the insular cortex is a brain region where contextual information about the environment and the self are bound together. The insular cortex sends this information to the prefrontal cortex, which is one of the final brain areas involved in making decisions. Because our internal states can shape our decisions, we hypothesized that connections between the insula and prefrontal cortex would be necessary for social responses to others in distress.” 

In a task where rats were exposed to either stressed pups or adult peers, rats tended to approach juveniles while avoiding adults. The ability to make these social decisions required both the prefrontal cortex and insula, as well as intact signaling between these areas. The researchers theorize this signaling may mean that rats find the presence of a distressed pup a more urgent social situation requiring less evaluative effort and quicker action than a situation involving a distressed adult peer, whose reason for being distressed may be more unclear to the rats. 

Addressing remaining unknowns, says Christianson, “We know that when you take the pathway away, it affects behavior. But we can’t tell exactly what information is relayed from the insula to the prefrontal cortex. We plan to record neural activity in these regions seeking to decode which aspects of social encounters are processed in this circuit. Is it stress? Age? Threat? Or all of the above?” This work may ultimately help with developing treatment strategies for psychiatric conditions characterized by social anxiety or trauma, according to the authors. 

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Please contact media@sfn.org for full-text PDF. 

About JNeurosci 

JNeurosci was launched in 1981 as a means to communicate the findings of the highest quality neuroscience research to the growing field. Today, the journal remains committed to publishing cutting-edge neuroscience that will have an immediate and lasting scientific impact, while responding to authors' changing publishing needs, representing breadth of the field and diversity in authorship. 

About The Society for Neuroscience 

The Society for Neuroscience is the world's largest organization of scientists and physicians devoted to understanding the brain and nervous system. The nonprofit organization, founded in 1969, now has nearly 35,000 members in more than 95 countries. 

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Journal

JNeurosci

DOI

10.1523/JNEUROSCI.1747-25.2026 

Article Title

Insular Input to the Prelimbic Cortex Underlies Social Affective Behavior in Rats

Article Publication Date

4-May-2026

 

Can dopamine bend time to shape memory?

The brain may use dopamine to expand time between distinct events, enabling us to remember unique episodes.

University of California - Los Angeles

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Key takeaways

• Why do we often recall events as lasting longer or shorter than they did? New research by UCLA psychologists shows that dopamine signaling at event beginnings may stretch time in our memory. 

• A key dopamine-producing area of the brain — the ventral tegmental area — was activated when volunteers participating in an MRI scan detected the start of a new event. When this dopamine hub activated more strongly, people later reported more time had passed.

• The finding suggests that dopamine plays a role in breaking lived experience into meaningful segments that can be stored as memories.

Ever heard of getting a “dopamine hit” from something you enjoy? These exciting moments also appear to influence memory, although perhaps not in the way you’d expect.

New research by UCLA psychologists suggests your brain may use dopamine to distort and expand time between distinct events, separating the flow of experience into pieces that can be flexibly reconstructed in the future.

The study, published in Nature Communications, found that a key dopamine-producing area of the brain — the ventral tegmental area — was activated when volunteers participating in an MRI scan detected the start of a new event. Importantly, when this dopamine hub was strongly activated, people reported more time had passed. The researchers also found that when people blinked more during a new event — an action thought to be related to dopamine signaling — their memory for time once again expanded. 

“Dopamine is often talked about in the media as a chemical that makes things feel rewarding. People say we get a burst of dopamine when we eat food that we like, or when we scroll on social media, for example,” said first author and UCLA doctoral student Erin Morrow. “But the dopamine system in our brain also responds strongly to novelty and change. We found that activation of the dopamine system at the beginning of a new event is likely one of the ways that our brain segments experiences into memorable episodes.

How do we form durable memories from the steady flow of life’s experiences?

When we summon a memory, we may recall events as having unfolded very quickly or having dragged on at unbearable slowness. But that’s not actually how time elapsed in the moment. It’s somewhat of a puzzle, then, how our brain adds or subtracts time from the original flow of our experiences. This question is important because how our brain constructs new memories is related to how we experience and represent time.

UCLA psychology professor David Clewett studies how the brain marks event boundaries, which are transitions between different noteworthy contexts, to segment experience into a more organized format that can be retrieved later as memory.

“Time is often treated as a physical dimension,” said Clewett. “But in psychology, time isn’t fixed. It’s something the brain constructs and is shaped by experience. As my colleague, professor Dean Buonomano puts it, our sense of time is evolution’s way of allowing us to understand change. Our findings suggest that this process also shapes memory. I think of it as inserting small wedges into an otherwise continuous stream, helping neighboring events stand apart.”

“The purpose of memory is not always to reconstruct the past completely accurately,” said Morrow. “It helps us remember past experiences in the most useful way possible so that we can change our future behavior.”

The dopamine system is engaged when new events happen

Researchers asked 32 volunteers to look at pictures of neutral objects while inside an MRI scanner. In between each object, tones were played in either the right or left ear. The same tone was repeated in the same ear across eight consecutive items to create a sense of a coherent event. The tone then switched to the other ear and changed pitch to create an “event boundary,” a meaningful change that signaled the current event had ended and the next had begun.

This repeat-switch pattern continued throughout the remainder of the sequence, creating the perception of four different auditory events. Functional magnetic resonance imaging (fMRI) revealed strong activation of the ventral tegmental area (VTA) when changes occurred, suggesting that dopamine signaling was taking place. Stronger VTA responses were also associated with increased blinking, consistent with other evidence linking dopamine signaling to blinking.

Participants were then presented with pairs of images from the earlier sequence and asked how far apart in time they appeared. However, the “secret” was that the images were all actually the same distance apart in time. Strikingly, participants remembered items that spanned tone switches as occurring farther apart. This finding suggested that the tone switch — and the VTA response accompanying it — had helped separate the objects into different memories. If people blinked more often across this window, they also remembered the items as occurring further apart.

 “We think the time dilation effect we found is useful, even though it’s not accurate, because it may help push those experiences farther apart in memory,” said Morrow.

Morrow said that the literature on the relationship between blinking and dopamine is mixed. She pointed out that many studies focus on blinking at rest or in people living with disorders related to atypical dopamine levels. In contrast, the current study took the novel approach of looking at dopamine and blinking while people without diagnosed psychiatric disorders were actively perceiving events.

How does change mark time in human memory?

This study represents an important step toward understanding how dopamine shapes memory. However, there are a few important limitations. These brain scans can’t directly measure dopamine release, nor whether it causes time dilation directly. More research is needed to see whether these laboratory-based effects also apply to more complex, real-world experiences.

Even so, these findings could begin to shed light on why time feels so flexible and why it can differ so drastically across people and situations. Alongside novel or rewarding experiences, dopamine is also pumped across the brain during stress. This may help explain our strange memories of time during the COVID-19 pandemic. For many people, lockdown felt slow in the moment, yet occupies surprisingly little space in memory. Long stretches of Zoom meetings or online learning at home offered few contextual changes, leading those periods to later be indistinguishable and compressed. By contrast, the early periods of the pandemic – marked by stress and upheaval – often feel expanded in memory. Together, these examples demonstrate that when experiences are more eventful, the brain has more information to work with. 

“Perhaps most importantly, our findings suggest that we don’t simply move through time,” says Clewett. “It is something we help create. By embracing change and variety, we expand our memories and, in that sense, expand our lives.”

The research was funded by the National Institutes of Health.

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Journal

Nature Communications

 

The GLP-1 paradox: Rice study finds weight loss drugs may carry unexpected stigma

Rice University

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Glucagonlike peptide-1 (GLP-1) medications have taken over the national conversation around weight loss. From celebrity headlines to everyday conversations, GLP-1 drugs like Ozempic and Wegovy are often framed as breakthroughs and seen as powerful new tools that can help people lose significant weight.

But new research from Rice University suggests the social reality may be more complicated. In some cases, using these medications may come with more judgment than not losing weight at all.

That’s the surprising finding behind a new study from Erin Standen, assistant professor of psychological sciences at Rice, published in the International Journal of Obesity with co-authors Sean Phelan, professor of health services research at the Mayo Clinic, and Janet Tomiyama, professor of psychology at the University of California, Los Angeles.

“We expected there might be some stigma around using a GLP-1,” Standen said. “But what surprised us was the extent of it.”

In the study, participants were asked to evaluate a fictional person based on their weight history. The person either lost weight using a GLP-1 medication, lost weight through diet and exercise or did not lose weight at all. The results revealed a clear pattern. People viewed those who used GLP-1 medications more negatively than those who lost weight through traditional methods.

But the most striking finding went a step further.

Participants also rated the GLP-1 user more negatively than someone who had not lost weight at all.

“The GLP-1 users were socially penalized not just compared to someone who lost weight through diet and exercise,” Standen said. “They were also rated more harshly than someone who didn’t lose weight in the first place.”

The findings highlight a complicated reality. Stigma does not disappear with weight loss. It can simply take a different form.

“There’s this idea that if you lose weight, you might escape stigma,” Standen said. “But what we’re seeing is that people may face judgment at multiple points. They may be judged for their weight and for how they choose to manage it.”

That tension is especially relevant now as GLP-1 medications continue to grow in popularity and visibility. Much of the stigma appears tied to perception.

“There’s a narrative that using these medications is ‘taking the easy way out,’” Standen said. “And that belief seems to shape how people are judged.”

What happens when the weight comes back

The study also explored another increasingly common scenario. What happens when someone stops taking a GLP-1 medication? Because of cost, insurance limitations or side effects, many people discontinue use. When that happens, they often regain weight. Standen’s research found that this also comes with social consequences.

Participants rated individuals who regained weight, whether after using a GLP-1 or after dieting, more negatively than those who lost weight and kept it off.

“There’s a lot of stigma tied to weight regain in general,” Standen said. “And that doesn’t seem to depend much on how the weight was lost in the first place.”

For Standen, the findings point to something deeper than social attitudes.Weight stigma has been consistently linked to negative mental and physical health outcomes. These include stress, avoidance of medical care and unhealthy coping behaviors.

“If people feel judged for the choices they’re making about their health, that can influence what they’re willing to do,” she said. “It can affect whether they seek care, whether they talk openly with providers and how they manage their health overall.”

That concern is particularly important as GLP-1 medications become more widely used and more widely discussed.

“This is a moment where these treatments are really entering the mainstream,” Standen said. “So understanding the social side of that is critical.”

Standen’s work fits into a broader research focus on how to promote health without reinforcing stigma. She said er goal is to better understand how people can be supported in making healthy choices without feeling judged in the process.

“There’s such a strong cultural script around weight and what a ‘healthy’ body should look like,” she said. “And those messages can get in the way of people doing what’s actually best for them.”

She said she hopes the research helps shift that narrative.

“Ultimately, any form of stigma related to someone’s body or their health choices is not helpful,” Standen said. “People should be able to make decisions that are right for them without fear of being judged.”

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Journal

International Journal of Obesity

DOI

10.17605/OSF.IO/7FM2R 

Method of Research

Randomized controlled/clinical trial

Article Title

An experimental investigation of the stigmatization of weight loss and regain from GLP-1 receptor agonist use and cessation

CRIMINAL CAPITALI$M

Minor federal fines offer little deterrence to insurers for Medicare Advantage violations, study finds

Using newly obtained federal data, Brown health policy researchers provide one of the clearest looks at how federal regulators impose Medicare Advantage penalties over a 13-year period, and how they fail to.

Brown University

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A new study from health policy researchers at the Brown University School of Public Health suggests that while regulators have several tools at their disposal to penalize insurance plans that break the rules, they rely mostly on relatively small financial penalties that may do little to deter violations.

The study, published in JAMA Internal Medicine, raises questions about how effectively federal regulators — primarily the Centers for Medicare & Medicaid Services — are overseeing the fast-growing Medicare Advantage industry and protecting patients, according to researchers from Brown’s Center for Advancing Health Policy through Research.

 “Nobody really knows how this regulatory authority has been imposing its different enforcement tools over the past decade,” said lead study author Zihan Chen, a Brown doctoral student in health services research. “The study was to address this kind of gap and begin to really understand how the federal government is overseeing Medicare Advantage and using its enforcement actions as a tool to punish or deter kinds of violations.”

The data for the study was obtained as through a Freedom of Information Act request and examines enforcement actions against Medicare Advantage insurers from 2010 through 2023 following violations such as inappropriately denying or delaying covered care.

Zihan said the research team was interested in examining CMS oversight because Medicare Advantage, the private alternative to traditional Medicare, now covers more than half of all Medicare beneficiaries in the U.S. and represents a major share of federal health spending. There have also been various formal complaints about Medicare Advantage insurers from beneficiaries, such as aggressive marketing and burdensome prior authorizations.

As the primary regulator, CMS has several enforcement tools, including the ability to terminate contracts, suspend plans from enrolling new members or marketing their products, and issue financial penalties.

The new analysis found that in practice, CMS rarely used its most severe tools and instead relied overwhelmingly on fines. Of 844 enforcement actions identified over the 13-year period, 87% were monetary penalties, while suspensions accounted for about 12%. Contract terminations made up less than 1%.

Even when fines were imposed by CMS, they were relatively small, peaking at about $6.50 per enrollee in 2019. Most other years they were under $3 per enrollee. While these figures could add up to millions of dollars overall, they are still small compared to the thousands of dollars insurers receive per patient each year. The researchers say it appears these amounts do little to change behavior.

“When fines are levied on plans, it almost means nothing compared to the profits the plans are making. This raises questions about meaningful consequences for violations,” said David Meyers, an associate professor of health services, policy and practice at Brown. “It supports a narrative out there that the government is a little bit asleep at the wheel when it comes to actually regulating the program that they have responsibility for.”

The findings also show that enforcement activity is uneven over time, often clustering around CMS audit cycles, suggesting that violations are more likely to be identified during scheduled reviews than during routine monitoring.

Other findings include differences in the types of plans facing enforcement. For example, contracts that were suspended or terminated tended to have lower quality ratings and served higher shares of low-income and minority beneficiaries, raising concerns that disruptions caused by enforcement may disproportionately affect vulnerable populations.

The research team makes clear in the study that enforcement actions by CMS were not rare. About 42% of Medicare Advantage contracts received at least one enforcement action during the study period and about one in five faced multiple actions, mainly the small fines.

Meyers says the reliance on smaller penalties reflects, in part, how CMS has designed its enforcement system.

“They have the authority to do more, but they’re choosing not to,” he said.

Other factors, such as limited resources, legal risks and resistance from insurers, may also shape how aggressively the agency enforces rules, Meyers added.

By assembling more than a decade of records, the new study is one of the first to examine long-term trends in Medicare Advantage enforcement.

“The Medicare Advantage program is so big and so important, but there’s very little enforcement action that seems to be going on to address challenges that have been widely reported,” Meyers said.

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Journal

JAMA Internal Medicine

DOI

10.1001/jamainternmed.2026.1237 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Federal Enforcement Actions Against Medicare Advantage Plans

Article Publication Date

4-May-2026