Why am I always cold on Mounjaro?
Feeling cold isn't listed as a side effect in the UK leaflet for Mounjaro (tirzepatide), and we found no study testing whether it causes it. Mounjaro reduces how much people eat, and in a 6-month diet trial without medicine, a 25% calorie cut lowered core body temperature. Feeling cold more than usual is a common sign of an underactive thyroid.
Is feeling cold a side effect of Mounjaro?
Feeling cold, chills and low body temperature don't appear anywhere in the UK Mounjaro leaflet or SmPC, both revised in August 2026.1,2
The nearest listed effects are tiredness (fatigue), which is common or very common. Dizziness and low blood pressure are common in people using it for weight loss.1 The UK SmPC for Wegovy (semaglutide) doesn't mention feeling cold either.3
The leaflet asks you to report unlisted side effects to the Yellow Card scheme, as our Yellow Card answer explains.1 Every listed effect is in Guide 5: side effects and risks.
Could eating less be the reason?
Possibly, because in diet studies without any medicine, eating fewer calories went with a lower core body temperature.4,5
A 6-month US trial split 48 healthy adults, overweight but not obese, into 4 groups. Core body temperature fell in the group that cut calories by 25%.4
A second study measured 24 lean, weight-stable adults who had eaten less for an average of 6 years. Their core temperature was lower than in 48 people eating a typical Western diet, including lean people who did endurance exercise. The authors said this was likely due to eating less, not to being leaner.5
Mounjaro (tirzepatide) lowers appetite and how much people eat.1,6 But we found no study that measured body temperature or feeling cold on Mounjaro, so the link is still a guess. In mice, a related medicine (liraglutide) injected into the brain raised heat production in brown fat, which points the other way.7
What could a GP check?
The NHS lists feeling cold more than usual as a common sign of an underactive thyroid, which a GP can check with a blood test.8
Low iron is another worry. The NHS signs of iron deficiency anaemia (too few red blood cells) are tiredness, breathlessness, palpitations and paler skin. Feeling cold isn't on its list. A GP checks for it with a full blood count.9
Fingers or toes that turn white, blue or red in the cold may be Raynaud's. The NHS says to see a GP if it starts for the first time after age 30.10
One 2026 case report described a 54-year-old woman on semaglutide who lost 22 kg in 4 months and, over that time, began to feel cold and tired. One of her thyroid hormones (T3) was low. Her symptoms went once her weight settled and she ate more.11 A single case can't show that semaglutide caused it.
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What do people on Mounjaro and similar medicines report about feeling cold?
From public patient forums: 9 Reddit threads in r/Zepbound, r/Mounjaro, r/Semaglutide and r/WegovyWeightLoss, read in October 2026. Personal reports, not medical evidence.
What people describe
- Not studied Most say they feel far colder than before, often in the hands and feet, even in warm rooms. We found no study of it, and the UK leaflet doesn't list it.1
- Not studied Many say the cold began in the first days or weeks, before much weight came off. So they blame the medicine, not fat loss. We found no study comparing the two.
- Not studied Several say it is worst a day or two after each injection, or comes back after a dose increase. We found no study of this timing.
- Not studied Several say it eased with time, once their weight was steady, on a lower dose or when they ate more. A few say it never eased. We found no study of either.
Advice people share
- Matches the NHS (thyroid) Several replies say to ask a GP for thyroid and iron blood tests. The NHS lists feeling cold as a common sign of an underactive thyroid, which a GP can test for. Feeling cold isn't on its list of anaemia signs.8,9
- Not studied Many use heated blankets, thermal layers, wool socks and hot drinks. People report this helps; we found no study of it.
- Label says otherwise A few say to eat something when very cold, in case blood sugar is low. The UK leaflet lists low blood sugar as very common with insulin or a sulphonylurea, and common with some other diabetes medicines. Its list of signs includes sweating but not feeling cold. The NHS says it's rare without diabetes.1,13
- Label says otherwise Several posts treat eating very little as normal. The UK leaflet says Mounjaro is used together with a reduced-calorie diet and more physical activity for weight loss.1
When should you get help?
See a GP if feeling cold comes with tiredness, breathlessness or paler skin than usual, which the NHS lists as signs of anaemia.9
Contact NHS 111 if you're more short of breath than usual, or have palpitations (a racing, skipping or fluttering heartbeat).12
- severe difficulty breathing: gasping, choking or not able to get words out12
- a chest that feels tight or heavy12
- lips or skin turning very pale, blue or grey12
- sudden confusion12
- signs that you may have hypothermia, a body temperature below 35C: shivering, pale, cold and dry skin, slurred speech, slow breathing, or tiredness or confusion14
Read the full picture
Related questions
Sources
- Eli Lilly. Mounjaro KwikPen (tirzepatide) UK patient information leaflet, last revised Aug 2026, sections 1, 2 and 4. UK label. medicines.org.uk (emc)
- Eli Lilly. Mounjaro KwikPen (tirzepatide) UK summary of product characteristics (SmPC), date of revision 29 Aug 2026, section 4.8. UK label. medicines.org.uk (emc)
- Novo Nordisk. Wegovy 2.4 mg FlexTouch (semaglutide) UK SmPC, date of revision 09/2026, section 4.8. UK label. medicines.org.uk (emc)
- Heilbronn LK et al. Effect of 6-month calorie restriction on biomarkers of longevity, metabolic adaptation, and oxidative stress in overweight individuals: a randomized controlled trial. JAMA 2006;295(13):1539-48. DOI 10.1001/jama.295.13.1539. PMID 16595757. People without obesity medicines. PubMed
- Soare A et al. Long-term calorie restriction, but not endurance exercise, lowers core body temperature in humans. Aging (Albany NY) 2011;3(4):374-9. DOI 10.18632/aging.100280. PMID 21483032. PubMed
- Heise T et al. Tirzepatide reduces appetite, energy intake, and fat mass in people with type 2 diabetes. Diabetes Care 2023;46(5):998-1004. DOI 10.2337/dc22-1710. PMID 36857477. Most authors work for Eli Lilly. PubMed
- Beiroa D et al. GLP-1 agonism stimulates brown adipose tissue thermogenesis and browning through hypothalamic AMPK. Diabetes 2014;63(10):3346-58. DOI 10.2337/db14-0302. PMID 24917578. Study in mice. PubMed
- NHS. Underactive thyroid (hypothyroidism) (page last reviewed 28 Apr 2025). nhs.uk
- NHS. Iron deficiency anaemia (page last reviewed 26 Jan 2024). nhs.uk
- NHS. Raynaud's (page last reviewed 20 Jul 2023). nhs.uk
- Elmezayen ZW et al. Euthyroid sick syndrome precipitated by rapid weight loss following semaglutide initiation: a case report. Clin Med Insights Endocrinol Diabetes 2026;19. DOI 10.1177/11795514261443862. PMID 42052217. One patient. PubMed
- NHS. Shortness of breath (page last reviewed 30 Jan 2024). nhs.uk
- NHS. Low blood sugar (hypoglycaemia) (page last reviewed 3 Aug 2023). nhs.uk
- NHS. Hypothermia (page last reviewed 9 Jun 2023). nhs.uk
Last checked 19 Oct 2026 · Next review due 19 Oct 2027 · Report an error
How this answer was made. Written by the GLP Guidebook team from the sources above. It's general information, not medical advice. The 'What people report' section summarises public patient forum posts we read; it is not medical evidence, and we never pass on advice that goes against the label. Talk to a qualified doctor before starting, stopping or changing any medicine. How we write