Most people starting Wegovy, Ozempic or Mounjaro are focused on weight loss. But researchers have increasingly discovered that GLP-1 medications do far more than suppress appetite. One of the more surprising areas of research concerns the immune system — how these medications interact with immune cells, reduce chronic inflammation, and may have a role in autoimmune and infectious conditions.

Here is what the current science tells us.

Do GLP-1 receptors exist on immune cells?

Yes — and this is the key to understanding why GLP-1 medications affect immunity at all. GLP-1 receptors (GLP-1R) have been identified on a range of immune cell types, including:

This means GLP-1 medications are not acting purely through the nervous system and pancreas. They are capable of directly modulating how your immune cells behave.

How do GLP-1 medications reduce inflammation?

Chronic low-grade inflammation is a hallmark of obesity and is tightly linked to insulin resistance, cardiovascular disease, and many other conditions. GLP-1 medications appear to fight this inflammation through multiple mechanisms:

Shifting macrophage behaviour

Macrophages exist in two broad states: the inflammatory M1 state and the anti-inflammatory M2 state. In obesity, macrophages — particularly in fatty tissue — tend towards M1, driving chronic inflammation. Research published in Nature Communications (2023) and subsequent studies have shown that GLP-1 receptor activation shifts macrophages towards the M2 phenotype, reducing the release of pro-inflammatory cytokines like TNF-α, IL-6, and IL-1β.

Lowering C-reactive protein (CRP)

The landmark SELECT cardiovascular trial, which enrolled over 17,500 people, found that semaglutide (the active ingredient in Wegovy and Ozempic) reduced high-sensitivity CRP — a key marker of systemic inflammation — by approximately 40%. Crucially, this reduction occurred partly independent of weight loss, suggesting a direct anti-inflammatory action of the drug itself.

Suppressing the NF-κB pathway

NF-κB is a molecular "master switch" for inflammation — when activated, it triggers a cascade of pro-inflammatory gene expression. Studies in animal models and in vitro (cell culture) have shown GLP-1 receptor activation can suppress NF-κB signalling in immune cells, dampening the overall inflammatory response.

What about autoimmune conditions?

People living with autoimmune diseases — conditions where the immune system attacks the body's own tissues — are often curious about what GLP-1 medications do to immune function. This is an area of active research with promising, if still early, findings.

Rheumatoid arthritis

Several observational studies have found that people with rheumatoid arthritis (RA) who take GLP-1 medications report reduced joint pain and lower disease activity scores. A 2024 register-based study from Denmark found lower rates of RA flares among GLP-1 users compared to matched controls. Researchers attribute this partly to weight loss — which reduces mechanical load on joints — and partly to the direct anti-inflammatory effects described above.

Multiple sclerosis

Intriguingly, GLP-1 receptors are also found on microglia, the immune cells of the central nervous system. Early-phase clinical trials and animal studies suggest that GLP-1 receptor agonists may reduce neuroinflammation and protect nerve tissue. However, evidence in humans with multiple sclerosis is still limited and large trials are ongoing. This remains a developing area.

Inflammatory bowel disease

The gut is home to a large proportion of the immune system, and GLP-1 is naturally produced in the gut lining (L-cells). Some small studies suggest GLP-1 agonists may have beneficial effects in Crohn's disease and ulcerative colitis, likely through modulation of gut macrophages and reduced intestinal inflammation. Clinical use in IBD is not yet established, but research is underway.

Does GLP-1 medication affect your ability to fight infections?

This is an important and nuanced question. The short answer is: for most people, GLP-1 medications do not impair the ability to fight infections, and may actually improve it in some cases.

COVID-19 outcomes

Multiple large-scale analyses during the COVID-19 pandemic found that people with diabetes or obesity who were taking GLP-1 medications had better outcomes from COVID-19 infection compared to those on other diabetes treatments. This included lower rates of severe disease, hospitalisation, and mechanical ventilation. The reasons are likely multifactorial: better glycaemic control, weight reduction, and direct immune-modulating effects.

Upper respiratory infections

Some clinical trial data suggest a modest increase in upper respiratory tract infections (common colds, sinusitis) in people taking semaglutide, though this was not consistently observed across all trials. If you do notice you are getting more colds, it is worth discussing with your doctor — though in most cases this is unrelated to immune suppression.

Injection site reactions

A small proportion of people develop redness, itching or swelling at the injection site — this is a local immune reaction, not a sign of impaired immunity. Rotating injection sites and ensuring good injection technique resolves this in most cases.

GLP-1, the gut microbiome, and immunity

The connection between GLP-1 and immunity extends to the gut microbiome. GLP-1 is produced by intestinal L-cells in response to food, and these same cells interact closely with the gut's immune environment. Research has shown that GLP-1 medications can alter the composition of the gut microbiome, generally shifting it towards bacteria associated with lower inflammation and better metabolic health. Since up to 70% of immune cells reside in the gut, this microbiome shift may represent an additional pathway through which GLP-1 medications modulate immunity.

What does this mean in practice?

If you are taking Wegovy, Ozempic or Mounjaro, here is what the current evidence suggests:

Conclusion

GLP-1 medications are far more than appetite suppressants. Through direct action on immune cells and indirect effects via weight loss, reduced blood sugar, and microbiome changes, they exert a meaningful anti-inflammatory effect. For many people — particularly those with obesity-related chronic inflammation, cardiovascular disease, or autoimmune conditions — this may represent an additional benefit of treatment. Research in this field is moving quickly, and the full immunological story of GLP-1 is still being written.

Always talk to your doctor before starting or adjusting any treatment related to immune function.

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