Does Mounjaro Make You Cold? UK Medical Guide

Many patients taking Mounjaro (tirzepatide) report feeling colder than usual, raising questions about whether this GLP-1 and GIP receptor agonist directly affects body temperature. Whilst cold intolerance is not listed as an adverse reaction in UK prescribing information, the sensation may be linked to rapid weight loss, reduced caloric intake, and metabolic changes associated with treatment. Understanding the mechanisms behind this experience and knowing when to seek medical advice can help patients manage symptoms effectively whilst continuing their diabetes or weight management therapy.

Understanding Mounjaro and Body Temperature Regulation

Mounjaro (tirzepatide) is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for the treatment of type 2 diabetes mellitus. Administered as a once-weekly subcutaneous injection, it works by enhancing insulin secretion in response to elevated blood glucose levels, suppressing glucagon release, and slowing gastric emptying. These mechanisms collectively improve glycaemic control and often lead to significant weight loss.

Body temperature regulation is a complex physiological process controlled by the hypothalamus, which maintains core temperature through metabolic heat production, peripheral vasoconstriction or vasodilation, and behavioural responses. Several factors can influence thermoregulation, including metabolic rate, thyroid function, body composition, nutritional intake, and certain medications. When the body undergoes rapid metabolic changes—such as those induced by weight loss medications—temperature perception may be affected.

Cold intolerance is not listed as an adverse reaction in the UK Summary of Product Characteristics (SmPC) for tirzepatide. However, anecdotal reports from patients have raised questions about whether the medication might contribute to feeling cold. Understanding the potential mechanisms behind this sensation requires examining how tirzepatide affects metabolism, body composition, and caloric intake. It is important to distinguish between genuine changes in body temperature and altered temperature perception, as these may have different underlying causes and clinical significance.

Why Some People Feel Cold on Mounjaro

Several physiological mechanisms may explain why some individuals taking Mounjaro report feeling colder than usual. The most significant factor is likely rapid weight loss, which commonly occurs with tirzepatide therapy. As body fat decreases, the insulating layer that helps maintain warmth is reduced, potentially leading to increased cold sensitivity. Adipose tissue serves not only as insulation but also as metabolically active tissue that contributes to heat production.

Reduced caloric intake represents another important consideration. Mounjaro significantly suppresses appetite through its action on GLP-1 receptors in the brain, leading many patients to consume substantially fewer calories. When energy intake decreases, the body may reduce its basal metabolic rate as an adaptive response, resulting in less heat generation through thermogenesis. This metabolic adaptation is a well-documented phenomenon during caloric restriction and weight loss.

There is no evidence from clinical trials that tirzepatide directly alters thyroid function. However, significant weight loss from any cause may affect thyroid hormone levels or peripheral conversion of T4 to T3 in some individuals, which could theoretically influence temperature regulation.

It is worth noting that dehydration or electrolyte imbalances—which can occur if patients experience gastrointestinal side effects such as nausea, vomiting, or diarrhoea—may also contribute to feeling cold. Proper hydration is essential for maintaining normal circulatory function and temperature regulation.

For persistent cold sensitivity, clinicians may consider assessing for other potential causes, including anaemia, hypothyroidism, or nutritional deficiencies that might develop during significant dietary changes.

Clinical Evidence: Cold Sensitivity as a Side Effect

A review of the pivotal clinical trials for tirzepatide, including the SURPASS programme for type 2 diabetes and the SURMOUNT trials for weight management, reveals that cold intolerance or feeling cold is not documented as an adverse reaction. According to the UK SmPC, the most frequently reported side effects are gastrointestinal in nature, including nausea (occurring in 12-22% of patients), diarrhoea, vomiting, constipation, and abdominal discomfort. These effects were generally mild to moderate and tended to diminish over time.

Cold sensitivity is not listed in the UK SmPC, and no published MHRA Drug Safety Updates have highlighted this as a safety signal. However, it is important to recognise that clinical trials may not capture all subjective experiences, particularly those that patients might not consider serious enough to report or that emerge only after prolonged use.

Interestingly, cold intolerance has been more consistently documented with other weight loss interventions, including bariatric surgery and very-low-calorie diets, where it is recognised as a common complaint. This suggests that the sensation of feeling cold may be more closely related to the weight loss itself rather than a direct pharmacological effect of tirzepatide.

That said, the absence of formal documentation does not invalidate patient experiences. Healthcare professionals should remain attentive to patient-reported symptoms and consider that individual responses to medication can vary considerably. If cold sensitivity is reported, a thorough clinical assessment should be undertaken to exclude other potential causes, such as anaemia, hypothyroidism, or nutritional deficiencies that may develop during significant dietary changes.

Managing Cold Sensations While Taking Mounjaro

For patients experiencing cold sensations whilst taking Mounjaro, several practical strategies may help improve comfort without compromising treatment efficacy:

Dietary and nutritional approaches:

• Ensure adequate caloric intake to support basic metabolic needs, working with a dietitian if necessary to develop a balanced eating plan

• Maintain sufficient protein intake as advised by a healthcare professional or dietitian, which helps preserve lean muscle mass that contributes to heat production

• Include warm foods and beverages throughout the day, such as soups, herbal teas, and cooked meals

• Ensure adequate intake of iron, vitamin B12, and folate, as deficiencies can contribute to cold intolerance

Lifestyle modifications:

• Dress in layers using natural, insulating fabrics such as wool or fleece

• Maintain regular physical activity, which increases metabolic rate and heat production; the UK Chief Medical Officers recommend at least 150 minutes of moderate-intensity activity weekly

• Stay well-hydrated, aiming for 1.5-2 litres of fluid daily unless otherwise advised by your healthcare provider (particularly important for those with heart or kidney conditions)

• Ensure adequate sleep, as sleep deprivation can affect metabolic function and temperature regulation

Monitoring and adjustment:

• Keep a symptom diary noting when cold sensations occur and any associated factors

• Discuss unexpectedly rapid or symptomatic weight loss with your prescriber

• Request blood tests to check thyroid function (TSH, free T4), full blood count, and nutritional markers if cold intolerance persists

It is important to continue taking Mounjaro as prescribed unless advised otherwise by your healthcare provider. Do not adjust the dose independently, as this may affect glycaemic control or weight management outcomes.

When to Seek Medical Advice

Whilst feeling slightly colder than usual during weight loss may be a benign adaptive response, certain symptoms warrant prompt medical evaluation. Contact your GP or diabetes specialist nurse if you experience:

• Severe or persistent cold intolerance that significantly affects daily activities or quality of life

• Additional symptoms suggesting thyroid dysfunction, such as extreme fatigue, constipation, dry skin, hair loss, depression, or unexpectedly slow heart rate

• Signs of anaemia, including pallor, breathlessness, dizziness, or unusual fatigue

• Symptoms of hypoglycaemia (low blood sugar), particularly if taking Mounjaro alongside insulin or sulphonylureas; these include tremor, sweating, confusion, and palpitations

• Unexplained weight loss exceeding expected rates or continuing beyond target weight

• Persistent gastrointestinal symptoms that may be causing dehydration or nutritional deficiencies

Seek urgent medical attention (call 999 or attend A&E) if you develop:

• Severe, persistent abdominal pain, which could indicate pancreatitis—a rare but serious side effect of GLP-1 receptor agonists. Stop taking tirzepatide and seek urgent medical attention if this occurs.

• Signs of severe dehydration, including reduced urine output, confusion, or rapid heartbeat

• Symptoms of severe allergic reaction, such as difficulty breathing, facial swelling, or widespread rash

If unsure whether it's an emergency, contact NHS 111.

Your healthcare team should conduct a comprehensive assessment including physical examination, thyroid function tests, full blood count, renal function, and review of your overall medication regimen. NICE guidance (NG28) recommends regular monitoring for patients with type 2 diabetes, typically including HbA1c checks every 3-6 months and annual review of complications and cardiovascular risk factors. If cold intolerance is accompanied by other concerning features, your clinician may consider whether Mounjaro remains the most appropriate treatment option.

Report any suspected side effects via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

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