The short answer
Probably not because of the drug itself. The adult labels for Ozempic, Wegovy, Mounjaro and Zepbound do not list colds, flu or a weakened immune system as side effects; the one infection-type entry in the adult Wegovy table is gastroenteritis, 6% versus 4% on placebo. What often changes on a GLP-1 is everything around it: far less food and protein, broken sleep, and the normal two to three colds a year adults get anyway. Those are worth fixing, and a fever that will not break or vomiting you cannot stop is worth a call.
At GLP-1 SOS this question shows up every fall: I have had three colds since I started, is my immune system shot? It is a fair worry when you are eating a fraction of what you used to. The honest answer has two parts: what the labels actually say, and what a much smaller plate and shorter nights can do.
At a glance
Three things to know
1
Not a listed side effect
Adult labels for semaglutide and tirzepatide do not list colds, flu or lowered immunity.
2
One gut exception
Gastroenteritis appears in the adult Wegovy table, 6% versus 4% on placebo.
3
The plate and the pillow
Less protein and fewer nutrients, plus short sleep, are the likelier links.
What the labels say, and what they do not
The adverse reaction tables list everything that happened more often on the drug than on placebo in the trials. In the Wegovy weight-loss trials in adults, no cold, sinus or flu entry appears. The infection-type items are gastroenteritis, 6% versus 4%, and viral gastroenteritis, 4% versus 3%. The label does not say why; some of what feels like a stomach bug may be the medicine’s own gut effects. The Zepbound and Mounjaro tables list no infections at all. In the Wegovy trial in teenagers, colds, sinusitis, flu and urinary infections did appear slightly more often, so the labels are not silent, but those figures come from adolescents, not adults.
So if the labels show no drop in defenses, why do so many people feel run down? Look at the inputs. A 2021 review of nutrition and immunity found that immunity is weaker in people who are malnourished or have low intakes of micronutrients, and that good nutrition supports the immune response. Eating half of what you used to for months, with protein the first thing to fall off the plate, can quietly push you toward that edge. Our page on how much protein to eat on a GLP-1 sets the target.
Lab note
Nothing in the adult labels points to weaker defenses. A plate with no protein and five-hour nights might.
Sleep matters more than people expect. In a study of 164 healthy adults who were given a cold virus on purpose, those who had slept less than six hours a night the week before were about four times as likely to develop a cold as those who slept more than seven. Nausea, reflux and night bathroom trips on a GLP-1 can cut nights short. Then there is the calendar: adults average two to three colds a year, mostly in winter and spring, so a few colds in your first GLP-1 winter may simply be a normal winter.
From the labels and studies
The numbers that matter
6% vs 4%
gastroenteritis on Wegovy 2.4 mg versus placebo in the adult weight trials, the only infection-type entry in that table
2 to 3
colds a year for the average adult, on or off a GLP-1, per MedlinePlus
About 4x
the odds of catching a cold after sleeping under six hours a night versus over seven, in a 2015 study of 164 adults
Sources: Wegovy Prescribing Information, June 2026; MedlinePlus, Common Cold; Sleep, 2015.
What to do
- Put protein back first. Something with protein at every meal, eaten first, even when the plate is small: eggs, yogurt, fish, chicken, tofu or beans. If you struggle to eat at all, talk to your prescriber; very low intake is a reason to slow down.
- Cover the nutrients you no longer eat. When meals shrink for months, zinc, vitamin D, iron and B12 can drift low. Ask for a blood test rather than guessing. GLP-1 SOS Daily Gut Relief is a digestive formula, not a cold remedy, but its 2 capsules with dinner include zinc and vitamin D alongside the magnesium, ginger and peppermint that support digestive comfort. A basic multivitamin covers those nutrients too.*
- Protect seven hours of sleep. A small, early dinner, the head of the bed raised if reflux wakes you, and caffeine kept to early in the day. In the 2015 study, the risk rose below six hours a night.
- Drink before you are thirsty. Many people drink less on a GLP-1, and a cold or fever raises fluid needs. Keep a bottle in sight and add broth or an electrolyte drink on sick days.
- Keep the usual protections. Hand washing, staying current on the vaccines your doctor recommends, and keeping your distance from sick people are the same advice for everyone, on or off a GLP-1.
- Have a sick-day plan. Know when to call if you cannot eat or drink, and what to do about your dose. Our page on GLP-1 and sick days: flu, stomach bug, antibiotics walks through it.
- Count real infections, not just bad weeks. If you have more than the usual two or three colds, infections that keep coming back, or frequent urinary symptoms, bring a list to your doctor. Our guide to UTIs and urinary changes on a GLP-1 covers that side.
*GLP-1 SOS Daily Gut Relief supports regular bowel movements and digestive comfort. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
Two kinds
Ordinary cold, or a call today
Usually ordinary
- Runny nose, sneezing, sore throat
- A cough that eases over a week or so
- Feeling tired while you are sick
- Two or three colds over a winter
Call the same day
- Vomiting or diarrhea you cannot keep up with
- Fever that lasts or climbs, or shaking chills
- Shortness of breath or chest pain
- Very little urine, dizziness when you stand
- Burning when you urinate with fever or back pain
A cold is a cold. Dehydration on top of a GLP-1 is not.
When to call your doctor
Call your prescriber the same day if:
- You are vomiting or have diarrhea and cannot keep fluids down
- You feel dizzy when you stand, or you are passing very little urine
- You have a high fever, a fever lasting more than a few days, or shaking chills
- You are short of breath, have chest pain, or a cough with fever that is getting worse
- You have burning when you urinate with fever or back pain
- You have severe belly pain that does not go away, with or without vomiting
- You take insulin or a sulfonylurea and cannot eat normally while sick
Colds come with winter. Dehydration, high fever or breathing trouble on a GLP-1 is a call, not a wait.
From the people behind the Lab
You do not have to figure this out alone.
GLP-1 SOS is the daily companion made for life on a GLP-1. Plain answers like this one, a support team that replies to real questions from real people, and daily formulas like GLP-1 SOS Daily Gut Relief, designed around the side effects that come with the medication. The GLP-1 Lab is our free education arm: no login, no paywall, no hype. Side effects are part of the road. Suffering through them is not.
Questions people also ask
Does Ozempic or Wegovy weaken your immune system?
The adult labels do not list a weakened immune system, colds or flu as side effects. The only infection-type entries in the adult Wegovy table are gastroenteritis, 6% versus 4% on placebo, and viral gastroenteritis, 4% versus 3%. What can weaken defenses is eating far less for months, especially protein, and sleeping poorly. Those are fixable and worth checking with your doctor.
Can Mounjaro or Zepbound make you catch colds more easily?
The Mounjaro and Zepbound adverse reaction tables do not list colds or other infections. If you seem to catch more colds, look at the usual suspects first: smaller meals with less protein, short or broken sleep, and the season, since adults average two to three colds a year. If infections keep coming back, ask your doctor to check your blood work.
Why do I feel so run down when I get sick on a GLP-1?
Because you are starting with less in the tank. Eating and drinking far less means smaller reserves of fluid and fuel, and many people drink less on a GLP-1 just when a fever raises fluid needs. Small, protein-first meals, steady sips of fluid and an early night help. If you cannot keep fluids down or feel faint when standing, call your prescriber the same day.
Should I take my GLP-1 shot when I have a cold?
The labels say nothing about colds specifically, so ask your prescriber what they prefer. The bigger question is whether you can eat and drink. If you have vomiting, diarrhea or a fever and cannot keep fluids down, call your prescriber before your next dose. Our page on GLP-1 sick days explains what to ask and when.
Do vitamins help me stop getting sick on a GLP-1?
Filling a real gap makes sense; extra-large doses have no proof behind them. A 2021 review found that immunity is weaker in people with low micronutrient intakes and that good nutrition supports the immune response. When meals shrink, protein, zinc, vitamin D, iron and B12 can run low, so a blood test is the best guide. Sleep, fluids and hand washing still count.
Sources (6)
- Wegovy (semaglutide) injection and tablets, Prescribing Information. Novo Nordisk / FDA, revised June 2026.
- Zepbound (tirzepatide) injection, Prescribing Information. Eli Lilly, revised August 2026.
- Mounjaro (tirzepatide) injection, Prescribing Information. Eli Lilly, revised August 2026.
- Common Cold. MedlinePlus, National Library of Medicine.
- Behaviorally Assessed Sleep and Susceptibility to the Common Cold. Sleep, 2015.
- Nutrition and immunity: lessons for COVID-19. European Journal of Clinical Nutrition, 2021.
Reviewed by the GLP-1 SOS editorial team · Education, not medical advice · Talk to your prescriber about your dose and your symptoms.
