GLP-1s and Your Immune System: Do These Medications Make You Sick More Often?

GLP-1 Receptors on Immune Cells: What the Research Shows

GLP-1 receptors (GLP-1R) are not limited to the pancreas and gut. They are expressed on several types of immune cells, and their activation produces measurable effects.

T Cells

GLP-1R expression has been identified on CD4+ and CD8+ T cells. A 2017 study in Nature Medicine found that GLP-1 receptor activation on T cells reduced the production of pro-inflammatory cytokines, including interferon-gamma (IFN-γ) and interleukin-17 (IL-17). These are cytokines associated with autoimmune inflammation. The effect was most pronounced in activated T cells, not resting ones, which suggests GLP-1s may dampen excessive immune responses without suppressing baseline immune surveillance.

Macrophages

Macrophages express GLP-1R, and activation shifts them from a pro-inflammatory M1 phenotype toward an anti-inflammatory M2 phenotype. A 2020 study in Cell Metabolism showed that GLP-1 receptor agonists reduced macrophage production of tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) by 30-40% in vitro. M2 macrophages are involved in tissue repair and resolution of inflammation, rather than pathogen destruction.

Dendritic Cells

Dendritic cells are the immune system's sentinels — they present antigens to T cells and initiate adaptive immune responses. GLP-1R expression has been documented on dendritic cells, and activation appears to reduce their capacity to present antigen and activate T cells. A 2019 study found that GLP-1 agonist treatment reduced dendritic cell expression of MHC class II and co-stimulatory molecules CD80 and CD86. This may contribute to reduced autoimmune activation, though it does not appear to impair infection-fighting capacity in clinical use.

Anti-Inflammatory Effects: Specific Cytokine Data

The anti-inflammatory effects of GLP-1s are among the most consistently documented immune-related findings.

C-Reactive Protein (CRP)

CRP is a general marker of systemic inflammation. Multiple trials have shown CRP reductions with GLP-1 treatment. The LEADER trial reported a 22% reduction in CRP with liraglutide compared to placebo over 3.8 years. The STEP 1 trial with semaglutide 2.4 mg showed a CRP reduction of approximately 40% from baseline at 68 weeks.

TNF-Alpha

TNF-α is a central pro-inflammatory cytokine. GLP-1 receptor agonists have been shown to reduce TNF-α production in macrophages and adipose tissue. A 2018 meta-analysis of 14 studies found that GLP-1 receptor agonist treatment reduced circulating TNF-α levels by an average of 15-25% compared to baseline.

Interleukin-6 (IL-6)

IL-6 drives both acute inflammation and chronic inflammatory conditions. Studies with liraglutide and exenatide have reported IL-6 reductions of 10-20% in patients with type 2 diabetes and obesity. The effect appears dose-dependent and correlates with weight loss magnitude.

These anti-inflammatory effects are one reason GLP-1s show cardiovascular benefits. Reduced vascular inflammation may contribute to lower rates of major adverse cardiovascular events. See our heart health article for more on this connection.

Autoimmune Conditions: Early Research

The anti-inflammatory properties of GLP-1s have prompted research into autoimmune diseases, where overactive immune responses drive pathology. The evidence so far is mixed but interesting.

Rheumatoid Arthritis (RA)

A small 2019 pilot study treated 12 RA patients with liraglutide for 12 weeks. Six patients showed improvement in DAS28 scores (a standard RA disease activity measure), while six did not. The responders tended to have higher baseline CRP. A separate 2021 animal study showed that GLP-1 agonist treatment reduced joint swelling and inflammatory cell infiltration in a collagen-induced arthritis model. Human data remains insufficient to draw conclusions.

Inflammatory Bowel Disease (IBD)

Research on GLP-1s and IBD has produced conflicting results. Some animal studies show GLP-1 agonists reduce intestinal inflammation and improve barrier function. However, a 2022 retrospective analysis of IBD patients on GLP-1 medications found no significant change in disease flares compared to controls. A 2023 case series reported 3 patients who developed new-onset colitis after starting semaglutide, but causality was not established. See our gut health article for more on GLP-1s and digestive conditions.

Multiple Sclerosis (MS)

Preclinical research has explored GLP-1 receptor agonists in experimental autoimmune encephalomyelitis (EAE), the animal model of MS. A 2020 study found that liraglutide reduced demyelination and microglial activation in EAE mice. No human trials in MS have been published yet. This remains an area of active investigation.

Infection Risk: Clinical Trial Data

The best data on infection risk comes from the large registration trials that tested GLP-1 medications for FDA approval.

STEP Trials (Semaglutide)

Across the STEP 1-5 trials, the most common infections reported were nasopharyngitis (common cold) and upper respiratory tract infections. In STEP 1, nasopharyngitis occurred in 10.7% of semaglutide patients versus 11.5% of placebo patients. Urinary tract infections occurred in 3.5% of semaglutide patients versus 3.1% of placebo patients. These differences were not statistically significant.

SURPASS Trials (Tirzepatide)

In SURPASS 1, the most frequently reported infections were nasopharyngitis (10.6% tirzepatide vs 9.2% placebo) and urinary tract infection (4.3% tirzepatide vs 3.6% placebo). In SURPASS 2, upper respiratory tract infections were reported in 5.5% of tirzepatide patients versus 5.1% of semaglutide patients. No infection signal emerged across the SURPASS program.

Pooled Analysis

A 2022 meta-analysis of 76 randomized controlled trials including over 46,000 patients found no significant increase in overall infection risk with GLP-1 receptor agonists compared to placebo or active comparators. The odds ratio for any infection was 1.03 (95% CI 0.99-1.08), which is not clinically meaningful.

Post-Market Surveillance: What FAERS Shows

The FDA Adverse Event Reporting System (FAERS) collects voluntary reports of adverse events after drug approval. FAERS data has limitations: reports are voluntary, unverified, and cannot establish causality.

That said, FAERS reports for GLP-1 medications do include infections, but they do not show a disproportionate infection signal compared to other drug classes. The most commonly reported immune-related events are injection site reactions (not true immune effects) and hypersensitivity reactions, which are rare.

A 2023 analysis of FAERS data for semaglutide found that infection-related reports were not significantly enriched compared to other diabetes medications. The reporting rate for infections was consistent with background population rates.

The Gut-Immune Connection

Approximately 70% of the body's immune cells reside in the gut-associated lymphoid tissue (GALT). The gut microbiome directly influences systemic immune function.

GLP-1 medications alter the gut microbiome. Studies show changes in the Firmicutes-to-Bacteroidetes ratio, increased Akkermansia muciniphila abundance, and reduced levels of pro-inflammatory bacterial taxa. These shifts may affect systemic immunity.

A 2021 study in Gut found that semaglutide treatment increased short-chain fatty acid (SCFA)-producing bacteria. SCFAs like butyrate support regulatory T cell function and intestinal barrier integrity. A stronger intestinal barrier reduces the translocation of bacterial endotoxins into the bloodstream, which reduces systemic inflammation.

The practical implication: GLP-1-related microbiome changes may support immune health over time, but the transition period may involve temporary gut disruption. See our gut health article for specific guidance on supporting your microbiome during GLP-1 treatment.

Vaccination Considerations

There is no evidence that GLP-1 medications reduce vaccine effectiveness. No clinical trial has specifically measured antibody titers after vaccination in GLP-1-treated patients versus controls.

However, there are practical considerations:

• Timing of GI side effects: GLP-1 injections commonly cause nausea, fatigue, and body aches in the 24-48 hours after a dose. If you receive a vaccine during this window, it can be difficult to tell whether symptoms are from the GLP-1 or the vaccine. Space your vaccination at least 3-4 days apart from a dose escalation.
• Dose escalation periods: During titration (the first 4-16 weeks of treatment), side effects are most pronounced. Schedule vaccinations during a stable dosing period when possible.
• No contraindication: GLP-1 medications are not a reason to delay or avoid any recommended vaccine, including influenza, COVID-19, pneumococcal, or shingles vaccines.

Nutrient Deficiencies and Immune Impact

When you eat less, you take in fewer vitamins and minerals. Several deficiencies that are common on GLP-1s directly affect immune function.

Vitamin D

Vitamin D supports T cell function, antimicrobial peptide production, and innate immune responses. Deficiency is widespread in the general population and may worsen on GLP-1s due to reduced dietary intake.

• Target range: 30-50 ng/mL (25-hydroxyvitamin D test)
• Deficiency threshold: Below 20 ng/mL
• Insufficiency threshold: 20-29 ng/mL

Ask your doctor for a 25(OH)D test, especially if you have limited sun exposure.

Vitamin B12

B12 is required for white blood cell production and proper immune cell function. GLP-1s may reduce B12 absorption through delayed gastric emptying and reduced dietary intake.

• Normal range: 200-900 pg/mL
• Deficiency threshold: Below 200 pg/mL
• Early depletion threshold: 200-300 pg/mL (may cause symptoms despite being "normal")

B12 deficiency on GLP-1s is well-documented. See our vitamins and supplements guide for supplementation details.

Zinc

Zinc is essential for neutrophil function, natural killer cell activity, and T cell development. Even mild zinc deficiency impairs immune response.

• Normal range: 70-120 mcg/dL (serum zinc)
• Deficiency threshold: Below 65 mcg/dL

Zinc losses increase with diarrhea, which is a common GLP-1 side effect. If you experience frequent GI symptoms, zinc status is worth checking.

Iron

Iron deficiency reduces T cell proliferation and impairs neutrophil bacterial killing capacity. Reduced food intake and decreased absorption can contribute to low iron on GLP-1s.

• Normal ferritin: 12-150 ng/mL (women), 12-300 ng/mL (men)
• Functional deficiency: Ferritin below 30 ng/mL with symptoms, even if hemoglobin is normal

Why You Might Feel Sick More Often

Understanding the research above, the most likely explanations for feeling sick more often on a GLP-1 are:

1. Nutrient Deficiencies

Reduced food intake means fewer vitamins and minerals. Deficiencies in vitamin D, zinc, B12, and iron can all impair immune function. These are correctable with supplementation and lab monitoring.

2. Dehydration

GLP-1s reduce thirst sensation. Chronic mild dehydration impairs mucosal barrier function (your first line of defense against respiratory pathogens) and reduces lymph circulation.

3. Physical Stress From Rapid Weight Loss

Significant caloric restriction and rapid weight loss are physical stressors. The body redirects resources toward maintaining essential functions, which may temporarily reduce immune reserves. This is similar to what athletes experience during intense training blocks.

4. Poor Sleep

If GLP-1 side effects (nausea, acid reflux, frequent urination) disrupt sleep, immune function suffers. Even one night of reduced sleep measurably decreases natural killer cell activity.

5. Coincidence

Timing matters. If you started GLP-1s during cold and flu season, the correlation may feel causal but isn't.

How to Support Your Immune System on GLP-1s

Immune support products:

• Vitamin D3 supplements — common deficiency on GLP-1s
• Zinc supplements — important for immune function
• Water bottle with time markers — stay hydrated on GLP-1s

1. Eat Nutrient-Dense Foods

When every bite counts, make it count:

• Colorful vegetables and fruits
• Lean proteins
• Whole grains
• Healthy fats (olive oil, nuts, avocado)

2. Supplement Strategically

If you're eating very little, a daily multivitamin can fill the gaps. Focus on the nutrients most likely to be low: vitamin D, B12, zinc, and iron. See our vitamins and supplements guide for specific product recommendations and dosing guidance.

3. Stay Hydrated

80+ oz of water daily. Add electrolytes if you're active or losing weight fast. Dehydration impairs mucosal immunity within hours.

4. Prioritize Sleep

Aim for 7-9 hours per night. If side effects are disrupting your sleep, address them. See our fatigue article for strategies to manage energy and sleep issues on GLP-1s.

5. Keep Moving

Moderate exercise boosts immune function. Even a daily 30-minute walk helps. Avoid overtraining, which can temporarily suppress immunity.

6. Get Lab Work Done

Ask your doctor to check:

• 25(OH) vitamin D
• B12 and methylmalonic acid
• Serum zinc
• Ferritin and complete blood count
• CRP (to track inflammation)

These are simple blood tests. Most insurance plans cover them annually. If you've been on a GLP-1 for more than 3 months and haven't had labs drawn, schedule them.

7. If You Need Antibiotics

GLP-1s and antibiotics can be taken together, but GI side effects may compound. See our antibiotics safety guide for specific guidance on managing both medications.

When to See Your Doctor

• You're getting sick more than 3-4 times per year
• Infections are lasting longer than usual
• You're getting infections that are unusual or severe
• You're also experiencing extreme fatigue, weight loss beyond what's expected, or night sweats
• Your lab results show deficiencies in vitamin D, B12, zinc, or iron

The Bottom Line

GLP-1s do not suppress the immune system. They are not immunosuppressants. The research shows anti-inflammatory effects that may actually benefit immune regulation. GLP-1 receptor activation on T cells, macrophages, and dendritic cells reduces pro-inflammatory signaling without impairing infection-fighting capacity.

Clinical trial infection data from the STEP and SURPASS programs shows no increase in infection rates compared to placebo. FAERS post-market data does not indicate an infection signal.

If you feel sick more often on a GLP-1, the most likely causes are reduced nutrient intake, dehydration, poor sleep, and the physical stress of rapid weight loss — not the drug itself.

Your action items:

1. Get baseline labs checked: vitamin D, B12, zinc, ferritin, CRP
2. Take a multivitamin if you're eating significantly less
3. Stay hydrated — 80+ oz daily
4. Prioritize 7-9 hours of sleep
5. Schedule vaccinations during stable dosing periods, not during titration
6. See your doctor if infections are frequent, prolonged, or severe
7. Don't assume every cold is caused by your GLP-1 — but do address the modifiable factors that make you more susceptible

This article is for informational purposes only and does not replace medical advice. Always talk to your healthcare provider about frequent infections or immune concerns.

Found this helpful? Share it with someone on GLP-1s who keeps catching every bug going around.

Related Reading

• GLP-1 Weight Loss Plateau? Why the Scale Stops (And How to Restart)
• Stopping GLP-1: What Happens When You Quit
• Nausea Triggers & Management: What Sets It Off and How to Stop It