If you started Ozempic or Wegovy (semaglutide), a GLP-1 medication, and then caught several colds, it is reasonable to wonder whether the two are connected. Current clinical evidence does not show that GLP-1 receptor agonists increase overall infection risk. It also does not show that these medicines “boost” immunity.
That distinction matters. A medication can influence inflammatory pathways without weakening the body's ability to respond to infection — and a lower inflammation marker is not the same thing as a stronger immune system.
The short answer
GLP-1 receptor agonists are not classified or prescribed as immunosuppressants. In a 2025 systematic review and meta-analysis of 136 randomized trials involving 164,322 participants, GLP-1 treatment was associated with slightly lower rates of total infections and serious infections, not higher rates.
Those results are reassuring, but they do not prove that GLP-1 medications prevent infections. The analysis combined different drugs, doses, patient groups, comparators, and follow-up periods. The researchers also found that greater weight loss and better blood-sugar control were associated with lower infection risk, so several factors may help explain the result.
A separate large observational study of U.S. veterans with diabetes also found lower rates of several infection-related outcomes among GLP-1 users compared with some other diabetes treatments or usual care. Because this was not a randomized trial and the population was predominantly older men with diabetes, it cannot establish cause and effect or be applied automatically to every GLP-1 user.
What the evidence supports: there is no clear overall signal that GLP-1 therapy makes people catch more infections.
What it does not support: claims that GLP-1s prevent infection, strengthen immunity, or have no immune effects whatsoever.
Inflammation is not the same as immune suppression
The immune system uses inflammation to respond to injury and infection. Chronic, low-grade inflammation associated with obesity and type 2 diabetes is different from the short-term inflammatory response needed to fight a pathogen.
Researchers have found that GLP-1 receptor agonists can affect inflammatory signaling in laboratory and animal studies. Human trials have also measured changes in C-reactive protein (CRP), a broad marker of inflammation. In exploratory analyses of the STEP 1, 2, and 3 trials, semaglutide 2.4 mg lowered CRP more than placebo over 68 weeks. The CRP changes occurred alongside weight loss and improvements in metabolic measures.
This finding should be interpreted narrowly:
- CRP is a nonspecific marker; it does not measure whether someone can fight a cold or respond to a vaccine.
- Lower chronic inflammation does not automatically mean the immune system is “better.”
- Changes seen in cells or animals cannot establish an infection outcome in people.
Earlier claims that GLP-1 medicines selectively alter specific T cells, macrophages, or dendritic cells while preserving infection defense go beyond what clinical outcome data can prove. The more useful question for patients is whether infections actually occur more often — and current trial evidence says they do not overall.
What prescribing information shows
Official prescribing information is useful for understanding events reported during trials, but a listed event does not always mean the medicine caused it.
The current Wegovy prescribing information lists gastroenteritis among the overall common adverse reactions. Nasopharyngitis appears in the pediatric trial table (12% with Wegovy versus 10% with placebo), but not in the label’s overall list of adverse reactions reported by at least 5% of Wegovy-treated patients. It does not carry a warning for generalized immune suppression. More familiar adverse effects include nausea, diarrhea, vomiting, constipation, abdominal pain, headache, and fatigue.
This is why simply counting colds in one trial is not enough. Respiratory infections are common in the general population, and trial tables must be interpreted against the comparison group, study design, and statistical uncertainty. A symptom or diagnosis occurring after a dose is not, by itself, proof that the dose caused it.
The same caution applies to spontaneous adverse-event reports. The FDA explains that its Adverse Event Monitoring System reports can be incomplete or duplicated, do not prove causation, and cannot be used to calculate how often an event occurs. Claims that FDA reports show either an infection danger or an infection benefit need a properly designed analysis, not a raw report count.
Why you may feel sick more often
Feeling unwell and having an infection are not the same thing. Several common situations can make the cause difficult to distinguish.
Medication side effects can resemble illness
Nausea, diarrhea, vomiting, headache, and fatigue may feel like a stomach virus or other infection. Symptoms that recur after dosing may suggest a medication effect, but timing alone cannot confirm the cause.
An infection may be coincidental
Starting treatment during cold, flu, or COVID-19 season can create a strong impression that the medication caused an infection. Household exposure, work or school contact, travel, and underlying health conditions may be more relevant.
Eating less can affect nutritional adequacy
GLP-1 medications often reduce appetite and food intake. That can make it harder for some people to meet nutrition needs, particularly when side effects limit the range or amount of food they can tolerate. A 2025 retrospective study found diagnosed nutritional deficiencies in more than 20% of a large cohort during the year after GLP-1 initiation, but it could not show that the medication caused those deficiencies. The participants already had overweight, obesity, type 2 diabetes, or a combination of these conditions, and claims-based diagnoses can miss important clinical context.
This evidence supports individualized nutrition assessment when there are concerns. It does not support assuming that every GLP-1 user is deficient, ordering the same laboratory panel for everyone, or taking high-dose supplements “for immunity.”
The 2024 Endocrine Society guideline, for example, suggests against routine vitamin D screening in otherwise healthy adults, including adults with obesity. Testing may still be appropriate when a clinician identifies a specific indication.
Vomiting or diarrhea can cause fluid loss
Severe or persistent gastrointestinal symptoms can lead to dehydration. That is a recognized safety concern, but it should not be reframed as proof that GLP-1 medicines suppress mucosal immunity. There is no single fluid target that is right for every person; needs vary with body size, health conditions, activity, climate, and symptoms.
For practical help with common reactions, see our GLP-1 side effects guide and fatigue and energy guide.
What about autoimmune conditions?
Anti-inflammatory findings have prompted research into rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, and other immune-mediated conditions. Much of the early evidence comes from cells, animals, small cohorts, or retrospective databases.
That research is hypothesis-generating. It does not make semaglutide, tirzepatide, liraglutide, or another GLP-1 medicine a replacement for established autoimmune treatment. Anyone with an autoimmune condition should coordinate medication decisions with the clinicians managing both conditions.
For digestive concerns, see our GLP-1 gut health guide.
A safer response to frequent illness
If you feel that you are getting sick more often, focus on documenting the pattern rather than trying to “boost” your immune system:
- Note the symptoms, temperature, duration, exposures, and relationship to injection day.
- Review whether symptoms sound like a recognized medication side effect or a diagnosed infection.
- Tell your prescriber if side effects are keeping you from eating or drinking normally.
- Discuss diet quality or testing when symptoms, medical history, or intake suggest a specific concern.
- Avoid starting iron, zinc, vitamin D, or other high-dose supplements without an identified need; supplements can cause side effects and interact with medications.
- Follow ordinary infection-prevention and vaccination guidance appropriate to you.
Our vitamins and supplements guide explains why supplement decisions should be individualized. If you are prescribed an antibiotic, review the GLP-1 and antibiotics safety guide and confirm instructions with your prescriber or pharmacist.
When to contact a clinician
Contact your healthcare team if infections seem unusually frequent, severe, prolonged, or difficult to clear, or if medication side effects keep you from maintaining food or fluids. Seek urgent care for trouble breathing, confusion, fainting, signs of severe dehydration, or another rapidly worsening symptom.
Do not stop or change a prescribed GLP-1 medication solely because of a suspected connection. A clinician can review the timeline, consider other medicines and health conditions, and decide whether evaluation or a treatment change is warranted.
The bottom line
Current clinical evidence does not show that GLP-1 receptor agonists increase overall infection risk. A large randomized-trial meta-analysis actually found modestly lower infection rates, but that association should not be turned into a claim that these medicines prevent infections or “boost” immunity.
GLP-1 medicines can influence inflammation, and semaglutide has lowered CRP in clinical trials. Neither finding proves stronger or weaker immune defense. If you feel sick after starting treatment, medication side effects, an unrelated infection, reduced intake, and other health factors are all possibilities worth sorting out with a clinician.
This article is for informational purposes only and does not replace medical advice. Talk with your healthcare provider about frequent infections, persistent side effects, nutrition concerns, or vaccine decisions.
