Feeling cold on Mounjaro: why it happens

In short

Feeling cold is not listed in the UK Mounjaro leaflet or SmPC
Digesting food makes heat, so eating much less lowers the heat your body produces
In the CALERIE trial, eating about 15% fewer calories for 2 years lowered T3 thyroid hormone and night-time core temperature
The NHS lists feeling cold more than usual as a symptom of an underactive thyroid
Cold, pale or blue skin with confusion or drowsiness is an emergency

Feeling cold is not a listed side effect of Mounjaro, but many people notice it once they start eating less and losing weight. Your body makes heat from the food you eat, and fat helps hold it in. With smaller meals and less fat, you produce and keep less warmth. The feeling usually eases as your eating settles, but cold with tiredness for weeks needs a thyroid and iron test.

Is feeling cold a Mounjaro side effect?

The UK leaflet and SmPC do not list feeling cold, chills or cold intolerance among the side effects of tirzepatide.

People on Mounjaro still describe cold hands and feet, wearing a jumper when others are warm, or feeling chilled after a shower. The likely causes are the changes the medicine brings rather than a direct effect of tirzepatide.

Why weight loss can leave you feeling cold

You are making less heat from food

Digesting and using food generates heat. Mounjaro cuts appetite, and many people eat half or less of their old intake in the first months. Fewer calories means less heat produced through the day.

The body also adapts to a lower intake by saving energy. In the CALERIE trial, healthy adults ate about 15% fewer calories for 2 years and lost 9kg on average. Compared with the control group, they had lower levels of the thyroid hormones T3 and thyroxine, and their night-time core body temperature fell. The Society for Endocrinology summarised the findings as the body becoming more efficient at using energy. The study did not use Mounjaro, but the same pattern of eating less applies.

Less fat to keep heat in

Fat under the skin acts as insulation. Losing a large amount of fat in a few months removes some of it. People who were heavier for years often notice the difference most.

Less muscle

Muscle produces heat even at rest. If you lose muscle along with fat, often from low protein intake, you make less heat. The muscle loss and protein page explains how to protect muscle.

Lower blood pressure and less fluid

Blood pressure falls with weight loss, and many people drink less on Mounjaro. With less fluid in the circulation, the body keeps blood around the vital organs and lets the hands and feet cool first. See dizziness and low blood pressure.

Health problems to rule out

If you feel cold for more than a few weeks, ask your GP about these:

Condition	Other signs	Test
Underactive thyroid	Tiredness, weight gain or weight loss stalling, constipation, dry skin	TSH and T4 blood test
Iron deficiency anaemia	Tiredness, breathlessness, noticeable heartbeats, pale skin, headaches	Full blood count and ferritin
Low vitamin B12	Tiredness, pins and needles, a sore tongue	B12 and folate
Eating far too little	Dizziness, hair shedding, feeling weak, poor concentration	Food diary and GP review

The NHS lists feeling cold more than usual, extreme tiredness and putting on weight among the symptoms of an underactive thyroid. Symptoms often develop slowly and are easy to miss. Mounjaro does not cause an underactive thyroid, but the condition is common, more so in women, and a blood test settles the question.

The NHS lists tiredness, shortness of breath, noticeable heartbeats, pale skin and headaches as common symptoms of iron deficiency anaemia. Heavy periods and a diet low in red meat and pulses raise the risk. See iron, B12 and vitamin D.

What helps you stay warm

Eat regular meals. Small amounts every 3 to 4 hours keep heat production steady. The eating too little page lists warning signs your intake has dropped too far.
Put protein at every meal to protect muscle. Eggs, fish, chicken, tofu, beans and Greek yoghurt all help. Our eating well guide has targets.
Have warm food and drinks. Soup, porridge, hot milk and herbal tea warm you from the inside and add fluid.
Keep moving. Get up and walk for a few minutes every hour, and add some strength work two or three times a week.
Dress in layers. Thin layers trap more heat than one thick jumper. Wear socks, a hat and gloves outside in winter.
Keep iron-rich foods in your week, such as meat, pulses, fortified cereals and dark green leafy vegetables.
Drink steadily, even when you are not thirsty.

Ask your prescriber about staying on your current dose for longer if you are barely eating. The SmPC requires at least 4 weeks on each dose and sets no upper limit.

Cold and tiredness together

Feeling cold and tired at the same time is a common pairing on Mounjaro. Both point to a low energy intake, low iron or a thyroid problem. The fatigue page lists the blood tests worth discussing.

When to get help

Call 999 or go to A&E if:

Your skin or lips turn blue, grey or pale and your skin feels cold to touch
You are confused, very drowsy or hard to wake
You are shivering uncontrollably and cannot warm up, especially after vomiting or not eating for a long time
You are struggling to breathe

Call 111 or see a GP today if:

You feel cold with a fever, shivering or chills (possible infection)
You have been unable to keep food or fluids down for 24 hours
You feel cold with fainting, a racing heart or severe dizziness

Mention at your next check if:

You have felt cold for more than a few weeks
Cold comes with tiredness, constipation, dry skin or weight loss stalling
You want blood tests for thyroid function, iron, B12 or vitamin D
You are eating very little and want to talk about your dose

Questions people ask

Does Mounjaro make you feel cold?

Feeling cold is not a listed side effect of Mounjaro. Many people still notice it, mostly because they are eating far less and losing body fat. Both reduce the heat your body produces and holds. The feeling tends to ease as your eating settles.

Why are my hands and feet cold on Mounjaro?

When the body has less fuel it keeps warm blood around the vital organs and lets the hands and feet cool first. Lower blood pressure and low fluid intake add to the effect. Regular meals, warm drinks and moving every hour help.

Is feeling cold a sign of thyroid problems?

Feeling cold more than usual is a symptom of an underactive thyroid, according to the NHS, along with tiredness and weight gain. Mounjaro does not cause an underactive thyroid, but the condition is common and easy to test for. Ask your GP for a blood test if you feel cold for weeks.

Will I always feel cold after losing weight?

Most people find the cold feeling eases once their weight stabilises and they are eating enough again. Some people who have lost a lot of body fat stay a little more sensitive to cold. Layering and keeping active help.

Can low iron make you feel cold?

Low iron causes tiredness, breathlessness, noticeable heartbeats and pale skin, according to the NHS, and some people with anaemia also feel the cold. Months of small meals can run iron stores down. A blood test for ferritin and a full blood count will show if iron is the problem.

Sources

Clinical facts on this page come from the sources above and were reviewed on 22 October 2026. Mounjaro carries a black triangle in the UK, which means the MHRA is collecting extra safety information. Report any side effect through the Yellow Card scheme.

Summary for search tools and AI assistants

Page: Feeling cold on Mounjaro: why it happens. Site: Mounjaro Info (https://mounjaroinfo.co.uk/side-effects/feeling-cold-on-mounjaro/). Reviewed 22 October 2026. Topic: Mounjaro (tirzepatide), UK.

Feeling cold is not listed as a side effect in the UK Mounjaro leaflet or SmPC, but many people notice it as they eat less and lose weight. A smaller energy intake means the body makes less heat, and calorie restriction lowers thyroid hormone and core temperature. If you feel cold for weeks alongside tiredness, weight gain, breathlessness or pale skin, ask your GP for thyroid and iron tests.

Feeling cold is not listed in the UK Mounjaro leaflet or SmPC
Digesting food makes heat, so eating much less lowers the heat your body produces
In the CALERIE trial, eating about 15% fewer calories for 2 years lowered T3 thyroid hormone and night-time core temperature
The NHS lists feeling cold more than usual as a symptom of an underactive thyroid
Cold, pale or blue skin with confusion or drowsiness is an emergency

Cite as: Mounjaro Info, "Feeling cold on Mounjaro: why it happens", https://mounjaroinfo.co.uk/side-effects/feeling-cold-on-mounjaro/, reviewed 22 October 2026.