Feeling Cold on Mounjaro: Why It Happens and How to Stay Warm

Feeling cold on Mounjaro is something many patients mention, especially as the weather turns in autumn and winter. Cold hands, cold feet and reaching for an extra jumper are common experiences during significant weight loss.

However, feeling cold is not listed as a recognised side effect in the official prescribing information for tirzepatide. Therefore, it is usually a consequence of losing weight and eating less, not a direct action of the medicine. In this guide, Dr Emil Gadimali explains the likely causes, the warning signs that need a blood test and the practical steps that help.

In most cases, yes. Feeling colder than usual is a common and harmless response to eating fewer calories and carrying less body fat. As a result, the body produces less heat and holds on to it less effectively.

Nevertheless, persistent cold intolerance can occasionally point to a treatable problem, such as an underactive thyroid, iron deficiency or low vitamin B12. Consequently, if the feeling is severe, getting worse or accompanied by other symptoms, you should ask your doctor for a blood test.

Several separate mechanisms are involved, and they often act together.

Less heat from food. Digesting and processing a meal generates heat, a process known as diet-induced thermogenesis. Because Mounjaro reduces appetite, you eat less, and therefore you produce less of this heat.

A lower metabolic rate. A smaller body needs less energy. In addition, the body adapts to weight loss by conserving energy. A landmark study in the New England Journal of Medicine in 1995 found that maintaining a 10% lower body weight reduced total energy expenditure by more than body size alone would predict.

Less insulation. Subcutaneous fat acts as a layer of insulation beneath the skin. As that layer thins, heat escapes more easily. For example, many patients notice that a room they once found comfortable now feels cool.

Less muscle. Muscle generates heat, both at rest and during movement. Unfortunately, rapid weight loss can include some loss of lean tissue. In the SURMOUNT-1 body composition substudy, most of the weight lost on tirzepatide was fat, but a proportion was lean mass.

Lower fluid intake. Reduced appetite often comes with reduced thirst. Consequently, mild dehydration can reduce blood flow to the hands and feet and make them feel colder.

Of course, not everyone is affected equally. Generally, people who lose weight quickly, who started with less muscle, or who are eating very small portions notice the change most. Women also tend to report cold hands and feet more often than men.

In addition, the time of year matters. A patient who starts treatment in spring may notice nothing until the first cold week of autumn, when the missing insulation suddenly becomes obvious.

There is no good evidence that tirzepatide lowers core body temperature in humans. The Mounjaro Summary of Product Characteristics, approved by the MHRA, lists gastrointestinal effects such as nausea, diarrhoea and constipation as the most common side effects. Cold intolerance does not appear in that list.

In other words, feeling cold on Mounjaro is best understood as an effect of weight loss. Similarly, people who lose a comparable amount of weight through diet alone, or after bariatric surgery, frequently report the same sensation.

Furthermore, the timing usually supports this explanation. The cold feeling tends to appear after several weeks, once a meaningful amount of weight has been lost, and not within hours of an injection. By contrast, a true drug side effect such as nausea typically appears in the first few days after a dose or a dose increase.

Some patients do describe feeling shivery for a day or so after an injection. Often, this coincides with nausea and a very low food intake on that day. Therefore, eating something small and warm, and keeping up your fluids, usually settles it.

Most of the time no investigation is needed. However, some causes of cold intolerance are common, easy to test for and easy to treat.

Underactive thyroid. Hypothyroidism classically causes feeling cold, tiredness, dry skin, constipation and weight gain. Because several of these overlap with treatment effects, it can be missed. Therefore, a thyroid function test is sensible if the symptoms persist.

Iron deficiency. Low iron, with or without anaemia, is a well-recognised cause of cold hands and feet. It is more likely if you have heavy periods or eat very little red meat. Furthermore, eating less overall can lower iron intake.

Vitamin B12 and folate. Low levels can cause anaemia, tiredness, pins and needles and sensitivity to cold. In particular, people who also take metformin are at higher risk of low B12.

Our guide to vitamin and nutrient deficiencies on Mounjaro explains which nutrients are most often affected and how they are monitored. Additionally, a full blood count, ferritin, B12 and thyroid function can all be checked from a single sample.

At CutKilo, baseline and follow-up blood tests are part of supervised treatment. As a result, a deficiency can be identified early and corrected with diet or supplements before it causes significant symptoms.

Please contact a doctor promptly if feeling cold comes with any of the following.

• Marked tiredness, breathlessness or palpitations
• Fingers or toes that turn white, then blue, then red in the cold
• Dizziness or fainting when you stand up
• Shivering with a high temperature, which may indicate infection
• Very rapid weight loss, or eating so little that you feel weak
• Confusion, slurred speech or severe drowsiness

Fingers that change colour in the cold may indicate Raynaud’s phenomenon, which deserves a separate assessment. Moreover, if you are struggling to eat enough, your dose may need to be reviewed. As a result, your prescriber may pause the next dose increase or step the dose down.

Fortunately, simple measures make a real difference.

Eat regular, warm meals. Small, frequent meals keep heat production steadier than one large meal. For example, soups, stews and porridge are easy to tolerate when appetite is low.

Prioritise protein. Protein has the highest thermic effect of any nutrient, and it helps to protect muscle. Therefore, include a protein source at every meal.

Keep moving. Muscle activity is the body’s fastest source of heat. In addition, regular resistance training preserves the muscle that keeps your metabolic rate up. Our article on exercise on Mounjaro sets out a practical plan.

Drink enough fluid. Aim for regular warm drinks through the day. Consequently, circulation to your hands and feet is better supported.

Dress in layers. Several thin layers trap heat more effectively than one thick one. Likewise, warm socks, gloves and a hat reduce heat loss from the extremities.

Heat your home sensibly. The NHS advises heating the rooms you use most to at least 18C in winter. In particular, this matters for older adults and for people with heart or lung conditions.

For most patients, yes. The sensation tends to be strongest during the phase of fastest weight loss. Subsequently, as weight stabilises and food intake settles, the body adapts and the feeling usually eases.

However, some people remain a little more sensitive to cold at a lower weight than they were before. This is expected, and it is not harmful. Nevertheless, if the symptom is new, severe or out of keeping with your rate of weight loss, it is worth checking your bloods.

Importantly, do not respond by eating far less protein or skipping meals to speed up weight loss. Doing so reduces heat production further and increases the risk of muscle loss, tiredness and hair shedding. Instead, a steady rate of loss of around 0.5 kg to 1 kg each week is safer and far more comfortable.

Finally, keep a simple note of when you feel cold, what you had eaten and how you slept. Such a record helps your doctor to separate a normal response to weight loss from a pattern that needs investigation.

Feeling cold on Mounjaro is common, and it is usually the result of eating less and carrying less insulating fat. It is not a listed side effect of the medicine itself. However, the single most important takeaway is that persistent or severe cold intolerance deserves a simple blood test for thyroid function, iron and B12. In short, stay warm, eat enough protein, keep active and tell your doctor if the symptom does not settle.

Why are my hands and feet so cold on Mounjaro? The body protects its core temperature by reducing blood flow to the extremities. As a result, hands and feet feel cold first when heat production falls.

Is feeling cold a sign that Mounjaro is working? Not specifically. It reflects weight loss and lower food intake. Therefore, it is not a reliable measure of how well treatment is working.

Should I stop Mounjaro if I feel cold all the time? Do not stop without medical advice. Instead, speak to your prescriber, who can check your bloods and review your dose.

Can low iron make me feel cold on Mounjaro? Yes. Iron deficiency is a common cause of cold intolerance. Consequently, a ferritin test is worthwhile if the symptom persists.

Does feeling cold mean my thyroid is affected? Usually not. However, an underactive thyroid causes similar symptoms, so a thyroid function test is a sensible precaution.