Graves' disease and Mounjaro represent two distinct but potentially overlapping areas of medical management. Graves' disease, the leading cause of hyperthyroidism in the UK, affects thyroid hormone production and metabolism. Mounjaro (tirzepatide), a dual GIP/GLP-1 receptor agonist, is licensed for type 2 diabetes and weight management. Patients with Graves' disease may require Mounjaro for diabetes control or weight-related concerns, particularly following thyroid treatment. Understanding the safety, monitoring requirements, and potential interactions between these conditions is essential for effective clinical management. This article examines the evidence, UK guidance, and practical considerations for using Mounjaro in patients with Graves' disease.

Understanding Graves' Disease and Mounjaro

Graves' disease is an autoimmune condition and the most common cause of hyperthyroidism (overactive thyroid) in the UK. It occurs when the immune system produces antibodies that stimulate the thyroid gland to produce excessive amounts of thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3). This hormonal excess accelerates metabolism, leading to symptoms such as unintentional weight loss, rapid heartbeat, tremor, heat intolerance, anxiety, and in some cases, bulging eyes (thyroid eye disease). According to the British Thyroid Foundation, Graves' disease affects approximately 0.5-2% of the UK population and is more prevalent in women than men.

Mounjaro (tirzepatide) is a relatively new medication licensed in the UK for the treatment of type 2 diabetes mellitus and, more recently, for weight management in adults with obesity (BMI ≥30 kg/m²) or overweight (BMI ≥27 kg/m²) with weight-related comorbidities. It is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist. Mounjaro works by mimicking natural incretin hormones that regulate blood sugar levels, enhance insulin secretion when glucose is elevated, suppress glucagon release, slow gastric emptying, and reduce appetite. This dual mechanism makes it particularly effective for glycaemic control and weight reduction.

Patients with Graves' disease may develop type 2 diabetes independently or may experience weight gain following treatment for hyperthyroidism (with antithyroid drugs, radioactive iodine, or surgery), which can increase their risk of metabolic complications. Understanding how these two conditions and their treatments interact is essential for safe and effective management. According to the UK Summary of Product Characteristics (SmPC), there is no specific contraindication for using Mounjaro in patients with Graves' disease, but careful consideration of individual circumstances is necessary.

Can You Take Mounjaro If You Have Graves' Disease?

There is no absolute contraindication to using Mounjaro in patients with Graves' disease, according to the UK Summary of Product Characteristics (SmPC) for tirzepatide. However, the decision to prescribe Mounjaro must be individualised and based on a thorough assessment of the patient's thyroid status, diabetes control, overall health, and treatment goals.

Patients with active, uncontrolled hyperthyroidism should generally have their thyroid condition stabilised before initiating Mounjaro or any new medication for diabetes or weight management. Uncontrolled Graves' disease can cause significant metabolic disturbances, including elevated heart rate, increased metabolic rate, and cardiovascular strain, which may complicate the assessment of side effects or tolerability of new treatments. Additionally, hyperthyroidism itself can affect glucose metabolism, sometimes masking or altering the presentation of diabetes.

For patients whose Graves' disease is well-controlled on antithyroid medication (such as carbimazole or propylthiouracil), or who have achieved remission following radioactive iodine therapy or thyroidectomy, Mounjaro may be considered if clinically indicated for type 2 diabetes or weight management. It is crucial that prescribing clinicians review:

• Current thyroid function tests (TSH, free T4, free T3)

• Cardiovascular status and any history of arrhythmias

• Renal function, particularly if there are concerns about dehydration

• Pre-existing diabetic retinopathy, which requires close monitoring

• Concurrent medications and potential drug interactions

• Patient's ability to recognise and report symptoms of thyroid dysfunction or medication side effects

Important considerations before starting Mounjaro include:

• Pregnancy planning: Mounjaro is not recommended during pregnancy and should be discontinued at least 1 month before a planned pregnancy

• Oral contraceptive effectiveness may be reduced; additional contraceptive methods are advised for 4 weeks after starting treatment and after each dose increase

• Patients with severe gastrointestinal disease (e.g., gastroparesis) should generally avoid Mounjaro

• If the patient is on insulin, doses should not be rapidly reduced when starting Mounjaro, as this increases the risk of diabetic ketoacidosis

• Patients should be counselled to report symptoms suggestive of thyroid C-cell tumours (neck mass, difficulty swallowing, persistent hoarseness)

A collaborative approach involving endocrinologists, GPs, and diabetes specialists is often beneficial to ensure comprehensive care and monitoring.

Thyroid Monitoring and Blood Sugar Management

Patients with Graves' disease who are prescribed Mounjaro require regular monitoring of both thyroid function and glycaemic control. Thyroid hormone levels can fluctuate, particularly in the early stages of treatment or if medication doses are adjusted. According to the British Thyroid Association and NICE guideline NG145, thyroid function tests should be performed every 4–6 weeks during the initial treatment phase of Graves' disease, then every 2–3 months once stable, and at least 6-12 monthly for long-term follow-up.

When Mounjaro is introduced, it is important to maintain this monitoring schedule, as changes in metabolic rate associated with thyroid dysfunction can influence blood glucose levels. Hyperthyroidism tends to increase glucose production and can worsen glycaemic control, whilst hypothyroidism (which may develop if Graves' disease is overtreated) can reduce metabolic rate and potentially increase the risk of hypoglycaemia, particularly if the patient is also taking other glucose-lowering medications such as insulin or sulfonylureas.

Blood glucose monitoring should be intensified when starting Mounjaro, especially in the first few weeks. Patients should be educated on recognising symptoms of hypoglycaemia (sweating, tremor, confusion, palpitations) and hyperglycaemia (increased thirst, frequent urination, fatigue). Self-monitoring of blood glucose or continuous glucose monitoring may be appropriate depending on individual circumstances.

HbA1c should be measured at baseline and approximately every 3–6 months to assess long-term glycaemic control, in line with NICE guideline NG28. Renal function should be monitored at baseline and periodically, especially if the patient experiences severe gastrointestinal side effects that could lead to dehydration. If severe vomiting or diarrhoea occurs, patients should be advised to maintain hydration, seek medical advice, and consider temporarily withholding tirzepatide to prevent acute kidney injury.

Patients with pre-existing diabetic retinopathy should have regular ophthalmological assessments, as rapid improvement in glucose control can temporarily worsen retinopathy. Weight, blood pressure, and lipid profiles should also be monitored as part of comprehensive diabetes and cardiovascular risk management. Patients should be encouraged to maintain regular follow-up appointments and report any new or worsening symptoms promptly, as these may indicate changes in thyroid status or medication effects.

Side Effects and Drug Interactions to Consider

Mounjaro is generally well-tolerated, but like all medications, it can cause side effects. The most common adverse effects are gastrointestinal, including nausea, vomiting, diarrhoea, constipation, and abdominal discomfort. These symptoms are usually mild to moderate and tend to diminish over time as the body adjusts to the medication. Starting at a lower dose and gradually titrating upwards, as recommended in the prescribing information, can help minimise these effects.

Patients with Graves' disease may already experience gastrointestinal symptoms related to hyperthyroidism, such as increased bowel frequency or diarrhoea. It is important to differentiate between symptoms caused by thyroid dysfunction and those attributable to Mounjaro. If gastrointestinal side effects are severe or persistent, dose adjustment or temporary discontinuation may be necessary, and thyroid function should be reassessed.

Cardiovascular considerations are particularly relevant. Mounjaro can cause a modest increase in heart rate (typically 2–4 beats per minute on average), which may be of concern in patients with Graves' disease who already have tachycardia or atrial fibrillation. Patients with pre-existing cardiovascular conditions should be monitored closely, and any significant increase in heart rate or new cardiac symptoms should prompt urgent medical review.

Gallbladder disease is an important consideration. Tirzepatide has been associated with an increased risk of gallstones and cholecystitis. Patients should be advised to report symptoms such as right upper quadrant pain, fever, or jaundice promptly.

Regarding drug interactions, there is no direct pharmacokinetic interaction between Mounjaro and antithyroid medications such as carbimazole or propylthiouracil. However, Mounjaro delays gastric emptying, which can affect the absorption of oral medications. This includes oral contraceptives, which may have reduced effectiveness; additional contraceptive methods are recommended for 4 weeks after starting Mounjaro and after each dose increase.

Patients taking levothyroxine (if they have developed hypothyroidism post-treatment for Graves' disease) should take it consistently, ideally on an empty stomach in the morning, and thyroid function should be monitored to ensure adequate replacement.

For women of childbearing potential, it's important to note that Mounjaro is not recommended during pregnancy and should be discontinued at least 1 month before a planned pregnancy. It is also not recommended during breastfeeding.

There is no evidence to date linking Mounjaro with worsening of thyroid eye disease or other Graves' disease-specific complications, but any new ocular symptoms (pain, vision changes, increased proptosis) should be reported immediately and routine ophthalmic review should continue based on clinical need.

Patients should be advised to report any suspected side effects via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

When to Seek Medical Advice

Patients with Graves' disease taking Mounjaro should be vigilant for symptoms that may indicate complications or the need for medical review. Urgent medical attention is required if any of the following occur:

• Severe or persistent vomiting or diarrhoea, which can lead to dehydration and electrolyte imbalances

• Signs of hypoglycaemia (if taking other glucose-lowering medications): confusion, sweating, tremor, rapid heartbeat, or loss of consciousness

• Symptoms of worsening hyperthyroidism: significant weight loss, severe palpitations, chest pain, shortness of breath, or new-onset atrial fibrillation

• Symptoms of hypothyroidism: extreme fatigue, cold intolerance, significant weight gain, or depression

• Severe abdominal pain, particularly if radiating to the back, which could indicate pancreatitis (a rare but serious side effect of GLP-1 receptor agonists)

• Right upper quadrant pain, fever, or jaundice, which could indicate gallbladder problems

• Symptoms of diabetic ketoacidosis: abdominal pain, vomiting, rapid breathing, drowsiness, or fruity-smelling breath (particularly if insulin doses have been reduced)

• Changes in vision or eye symptoms: pain, redness, double vision, or worsening bulging of the eyes

• Allergic reactions: rash, itching, swelling of the face or throat, or difficulty breathing

Routine follow-up with your GP or endocrinologist should occur at least every 3–6 months, or more frequently if your condition is not yet stable. Blood tests to monitor thyroid function, HbA1c, kidney function, and lipid profile should be performed as recommended by your healthcare team.

For urgent concerns, contact NHS 111 for advice. For life-threatening symptoms such as severe chest pain, severe allergic reaction, or difficulty breathing, call 999 immediately.

Patients should maintain open communication with their healthcare providers and report any new symptoms or concerns promptly. It is also important not to stop or adjust medication doses without medical guidance, as this can lead to worsening of either diabetes or thyroid disease. If you are considering starting Mounjaro and have Graves' disease, discuss your full medical history, current medications, and treatment goals with your doctor to ensure a safe and personalised treatment plan.

Frequently Asked Questions