Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist licensed in the UK for type 2 diabetes treatment. Whilst gastrointestinal side effects such as nausea and diarrhoea are well-documented, some patients report concerns about swollen lymph nodes during treatment. Swollen lymph nodes (lymphadenopathy) are not listed as a recognised adverse effect in the UK Summary of Product Characteristics or clinical trial data. This article examines the evidence regarding Mounjaro and lymph node swelling, explores alternative causes of lymphadenopathy, and provides guidance on when medical evaluation is necessary.

Understanding Mounjaro and Its Common Side Effects

Mounjaro (tirzepatide) is a prescription medication licensed in the UK for the treatment of type 2 diabetes mellitus. A similar formulation of tirzepatide is authorised under the brand name Zepbound for weight management in adults with obesity or overweight with weight-related comorbidities. As a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist, Mounjaro works by enhancing insulin secretion when blood glucose levels are elevated, suppressing glucagon release, slowing gastric emptying, and reducing appetite. This dual mechanism contributes to improved glycaemic control and significant weight reduction.

Like all medications, Mounjaro is associated with a range of side effects, most of which are gastrointestinal in nature. According to the Summary of Product Characteristics (SmPC), the most commonly reported adverse effects include:

• Nausea and vomiting (very common) – particularly during dose escalation

• Diarrhoea or constipation (very common) – affecting bowel regularity

• Abdominal pain and discomfort (common) – often mild to moderate

• Reduced appetite (very common) – contributing to weight loss

• Dyspepsia (common) – indigestion or heartburn

• Injection site reactions (common) – such as redness or irritation

• Fatigue (common) – tiredness or lack of energy

These gastrointestinal symptoms typically diminish over time as the body adjusts to the medication. Hypoglycaemia risk is increased when Mounjaro is used alongside insulin or sulphonylureas, and dose reductions of these medications may be needed when starting tirzepatide.

According to the Medicines and Healthcare products Regulatory Agency (MHRA) and the SmPC, serious adverse effects are rare but may include pancreatitis, gallbladder disease, and allergic reactions. Patients with diabetic retinopathy should be monitored carefully, and severe gastrointestinal symptoms may lead to dehydration and acute kidney injury in susceptible individuals. Nutritional monitoring is important if appetite reduction is significant.

Understanding the established side effect profile of Mounjaro is essential when evaluating new or unusual symptoms during treatment, including concerns about swollen lymph nodes.

Can Mounjaro Cause Swollen Lymph Nodes?

Swollen lymph nodes (lymphadenopathy) are not listed as an adverse effect in the UK Summary of Product Characteristics (SmPC) or European Public Assessment Report (EPAR) for Mounjaro (tirzepatide). The pivotal SURPASS clinical trial programme, which evaluated tirzepatide's efficacy and safety in thousands of patients with type 2 diabetes, did not identify lymph node swelling as a recognised adverse effect. Similarly, the SURMOUNT trials examining tirzepatide for weight management did not report lymphadenopathy as a treatment-emergent adverse event.

The current evidence is insufficient to establish a causal link between tirzepatide and lymphadenopathy. The mechanism of action of tirzepatide—targeting GIP and GLP-1 receptors to regulate glucose metabolism and appetite—does not have a known direct effect on the lymphatic system.

It is worth noting that lymph node swelling can occur for many reasons unrelated to medication, including:

• Recent vaccinations (such as COVID-19 or influenza)

• Intercurrent infections (viral or bacterial)

• Local inflammation near injection sites

• Seasonal allergies or other immune responses

However, it is important to acknowledge that post-marketing surveillance continues to monitor for previously unrecognised adverse effects. Patients and healthcare professionals are encouraged to report any suspected side effects through the Yellow Card Scheme operated by the MHRA. This pharmacovigilance system helps identify rare or delayed adverse reactions that may not have been apparent during clinical trials.

If you develop swollen lymph nodes whilst taking Mounjaro, this symptom warrants medical evaluation to determine the underlying cause. The timing may be coincidental, and other explanations should be thoroughly investigated. It is essential not to assume causation without proper clinical assessment, as lymph node swelling can result from numerous unrelated conditions.

When Swollen Lymph Nodes Require Medical Attention

Swollen lymph nodes (lymphadenopathy) can be a normal immune response, but certain characteristics warrant prompt medical evaluation. Lymph nodes are small, bean-shaped structures that form part of the immune system, filtering lymph fluid and trapping bacteria, viruses, and other harmful substances. They commonly swell in response to infection or inflammation in nearby tissues.

You should contact your GP or healthcare provider if you experience:

• Persistent swelling lasting more than two to four weeks without improvement

• Progressive enlargement of lymph nodes over time

• Hard, fixed, or irregular nodes that do not move freely under the skin

• Nodes larger than 2cm in diameter (approximately the size of a grape)

• Swelling in multiple areas of the body simultaneously (generalised lymphadenopathy)

• Accompanying symptoms such as unexplained weight loss, drenching night sweats, or persistent fever

• Difficulty breathing or swallowing if nodes in the neck are significantly enlarged

• Skin changes over the lymph node, such as redness or warmth

• Supraclavicular lymphadenopathy (swollen nodes above the collarbone) – this requires urgent assessment

• You are over 40 years old with unexplained lymphadenopathy

• You are immunocompromised due to medication or underlying condition

Seek urgent medical attention (contact 111 or attend A&E) if:

• You develop severe difficulty breathing or swallowing

• You experience chest pain or signs of severe allergic reaction

• Lymph node swelling is accompanied by high fever and severe illness

In line with NICE guideline NG12 (Suspected cancer: recognition and referral), unexplained persistent or progressive lymphadenopathy, particularly with systemic symptoms, may warrant an urgent two-week referral to exclude malignancy.

Your GP will conduct a thorough clinical examination, taking a detailed history of your symptoms, recent infections, medications (including Mounjaro), and any other relevant health concerns. Depending on the findings, investigations may include blood tests, ultrasound imaging, or referral to a specialist for further evaluation. Early assessment ensures appropriate diagnosis and management, particularly to exclude serious underlying conditions that may require specific treatment.

Managing Side Effects While Taking Mounjaro

Effective management of side effects is crucial for maintaining adherence to Mounjaro therapy and achieving optimal therapeutic outcomes. Most adverse effects associated with tirzepatide are mild to moderate in severity and tend to improve with continued use as the body adapts to the medication.

Strategies for managing common gastrointestinal side effects include:

• Gradual dose escalation – following the prescribed titration schedule allows the digestive system to adjust, minimising nausea and vomiting

• Dietary modifications – eating smaller, more frequent meals; avoiding high-fat, spicy, or heavily processed foods; staying well-hydrated

• Timing of administration – some patients find that injecting Mounjaro at a consistent time, such as before bed, helps reduce daytime nausea

• Anti-emetic medication – if nausea is severe, your GP may consider short-term anti-sickness medication after clinical review. Note that metoclopramide has MHRA restrictions (maximum 5 days use, risk of extrapyramidal effects) and domperidone has cardiac risk warnings and contraindications. These should only be used at the lowest effective dose for the shortest possible duration

• Monitoring for dehydration – particularly important if experiencing vomiting or diarrhoea; seek medical advice if unable to maintain adequate fluid intake. Renal function should be checked if prolonged gastrointestinal symptoms occur, especially in those with existing kidney disease

For injection site reactions:

• Rotate injection sites (abdomen, thigh, upper arm) to prevent localised irritation

• Allow the medication to reach room temperature before injecting

• Use proper injection technique as demonstrated by your healthcare provider

Important safety considerations:

• Women using oral contraceptives should use non-oral or barrier methods for 4 weeks after starting tirzepatide and after each dose increase, as absorption may be affected

• If you are taking insulin or sulphonylureas, your doctor may need to reduce these doses to prevent hypoglycaemia

• Report symptoms of gallbladder disease (severe right upper abdominal pain, jaundice) promptly

• Attend all scheduled follow-up appointments to monitor glycaemic control, weight, and overall tolerability

• Report any new, persistent, or worsening symptoms to your healthcare team promptly

• Do not discontinue Mounjaro without consulting your prescriber, as abrupt cessation may affect diabetes control

• Be aware of signs of pancreatitis (severe, persistent abdominal pain radiating to the back) and seek immediate medical attention if these occur

Your healthcare provider can offer personalised advice based on your individual circumstances, comorbidities, and treatment goals. Open communication about side effects enables timely intervention and optimisation of your treatment regimen.

Alternative Causes of Lymph Node Swelling During Treatment

When lymph node swelling occurs during Mounjaro treatment, it is essential to consider alternative explanations, as numerous conditions can cause lymphadenopathy. Understanding these possibilities helps ensure appropriate investigation and management.

Common infectious causes include:

• Upper respiratory tract infections – colds, flu, COVID-19, or strep throat commonly cause cervical (neck) lymph node swelling

• Dental infections – abscesses or gum disease can lead to submandibular or cervical lymphadenopathy

• Skin infections – cellulitis, infected wounds, or insect bites may cause regional lymph node enlargement

• Viral infections – Epstein-Barr virus (glandular fever), cytomegalovirus, or HIV can cause generalised lymphadenopathy

• Bacterial infections – including tuberculosis, cat-scratch disease, or atypical mycobacterial infections

Non-infectious causes to consider:

• Recent vaccinations – COVID-19, influenza, or other vaccines can cause temporary lymph node swelling

• Reactive nodes near injection sites – local inflammation from any injection, including Mounjaro, may cause nearby lymph nodes to enlarge temporarily

• Autoimmune conditions – rheumatoid arthritis, systemic lupus erythematosus, or Sjögren's syndrome may present with lymph node swelling

• Medication reactions – certain drugs (not typically including GLP-1 receptor agonists) can rarely cause lymphadenopathy

• Malignancy – lymphoma, leukaemia, or metastatic cancer may present with persistent or progressive lymph node enlargement

• Sarcoidosis – a multisystem inflammatory condition that can affect lymph nodes

Coincidental timing:

It is important to recognise that starting a new medication like Mounjaro may coincide with the development of an unrelated condition. The temporal association does not necessarily imply causation. Many patients beginning diabetes or weight management treatment are undergoing lifestyle changes, increased healthcare engagement, or experiencing other health issues that may independently cause lymph node swelling.

Clinical evaluation by your GP will typically include:

• Detailed history of recent infections, vaccinations, travel, animal exposure, and constitutional symptoms

• Examination of the size, location, consistency, and mobility of affected lymph nodes

• Assessment for signs of infection, inflammation, or systemic illness

• Appropriate investigations such as blood tests, imaging, or specialist referral based on clinical findings

A thorough diagnostic approach ensures that the true cause of lymphadenopathy is identified and managed appropriately, whether related to infection, inflammation, or another underlying condition requiring specific treatment.

Frequently Asked Questions