Can you take Mounjaro with hypothyroidism?

Jump to: What is hypothyroidism? | How Mounjaro works | Hypothyroidism and weight | Taking Mounjaro with levothyroxine | Foods to focus on | Movement and hypothyroidism | Looking after your mental health | Mounjaro clinical data | Frequently asked questions | Take home message

You can take Mounjaro if you have hypothyroidism, but there are a few things to be aware of. Mounjaro slows gastric emptying, which can affect how your body absorbs levothyroxine (the standard treatment for an underactive thyroid), so timing your medications carefully matters.¹

Hypothyroidism affects around 2-3% of the UK population, with women significantly more likely to be affected than men.² Weight gain is one of the most common symptoms, and many people find it difficult to lose weight even when their thyroid levels are well controlled.

In clinical trials, people taking Mounjaro lost up to 26% of their body weight after two years.³ A 2023 conference abstract also suggested that tirzepatide may have a small beneficial effect on thyroid function, though this needs confirming in larger studies.⁴

This article covers how to take Mounjaro safely alongside levothyroxine, what the research says about thyroid function and weight, and practical guidance on food, movement, and mental health if you’re living with hypothyroidism.

What is hypothyroidism?

Hypothyroidism means your thyroid gland doesn’t produce enough thyroid hormones. The thyroid is a small gland in the front of your neck that produces hormones controlling metabolism, energy levels, and body temperature.²

The most common cause in the UK is Hashimoto’s thyroiditis, an autoimmune condition where the immune system gradually attacks the thyroid gland.²

Common symptoms include:

• Weight gain and difficulty losing weight
• Fatigue and low energy
• Feeling cold
• Dry skin and hair
• Constipation
• Depression and low mood
• Brain fog and poor concentration
• Muscle aches and weakness

Hypothyroidism is diagnosed with a blood test measuring TSH (a hormone that tells your thyroid how much to produce). High TSH means your thyroid isn’t producing enough, so your body is signalling it to work harder.²

Treatment is usually levothyroxine, a synthetic version of the thyroid hormone T4, taken once a day on an empty stomach. Most people need to take it for life, with regular blood tests to check their dose is right.²

How Mounjaro works

Mounjaro is a once-a-week injection that contains the drug tirzepatide. It works by mimicking two gut hormones, GLP-1 and GIP, that communicate with the brain’s appetite centre (the hypothalamus) to reduce hunger and food-seeking behaviour.

It also slows down digestion, so food stays in the stomach longer. This means you feel full sooner and stay satisfied for longer after eating.

In clinical trials, people taking Mounjaro lost up to 26% of their body weight after two years.³

This slowing of gastric emptying is the main reason medication timing matters if you’re taking levothyroxine alongside Mounjaro. We’ll cover exactly how to manage this below.

Hypothyroidism and weight

Weight gain is one of the hallmark symptoms of hypothyroidism. When your thyroid is underactive, your metabolism slows down, and your body burns fewer calories at rest.²

Even when hypothyroidism is well treated with levothyroxine and blood tests show normal thyroid levels, many people still struggle with their weight. This is partly because the metabolic effects of long-term hypothyroidism can persist, and partly because fatigue makes it harder to stay active.

There’s also a relationship between weight and thyroid function that runs in both directions. Obesity itself is associated with higher TSH levels, and weight loss can bring TSH levels down.⁴

This is where monitoring becomes important. As you lose weight on Mounjaro, your thyroid medication needs may change. Your GP or endocrinologist should check your thyroid levels regularly during weight loss and adjust your levothyroxine dose if needed.

Taking Mounjaro with levothyroxine

Levothyroxine is absorbed best on an empty stomach, ideally 30-60 minutes before eating.² Because Mounjaro slows gastric emptying, it’s worth being extra careful with timing to make sure your levothyroxine is absorbed properly.¹

The practical approach is straightforward:

• Take your levothyroxine first thing in the morning with water, at least 30-60 minutes before food or other medications
• Don’t take your Mounjaro injection at the same time of day as your levothyroxine
• If you inject Mounjaro in the morning, consider taking your levothyroxine at bedtime instead (at least two hours after your last meal), or vice versa

There’s no formal drug interaction listed between tirzepatide and levothyroxine. The concern isn’t a direct chemical interaction; it’s that slower gastric emptying could reduce how well your body absorbs the levothyroxine.¹

Getting your thyroid levels checked during weight loss

Weight loss itself can change how much levothyroxine you need. As you lose weight, your dose requirements may decrease, and taking too much levothyroxine can cause symptoms like a racing heart, anxiety, and difficulty sleeping.

Ask your GP to check your thyroid levels (TSH and free T4) every 8-12 weeks while you’re actively losing weight on Mounjaro, rather than waiting for your usual annual review. This is standard practice during significant weight change.

The MTC and MEN 2 contraindication

Mounjaro’s prescribing information includes a specific warning about thyroid cancer. In animal studies, tirzepatide caused thyroid C-cell tumours in rodents. It isn’t known whether this applies to humans, but as a precaution, Mounjaro is contraindicated in people with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).¹

MTC is a rare type of thyroid cancer, distinct from the more common papillary and follicular thyroid cancers. Having Hashimoto’s thyroiditis or standard hypothyroidism doesn’t increase your risk of MTC.

If you’re unsure about your thyroid history, speak to your prescriber before starting Mounjaro. They can check whether MTC or MEN 2 is relevant to you.

Foods to focus on with hypothyroidism

There’s no specific ‘thyroid diet’, but what you eat can support thyroid function, help manage fatigue, and work alongside Mounjaro to support healthy weight loss.

The goal is a balanced eating pattern built around whole foods that provide the nutrients your thyroid needs to function well.

Protein at every meal

Protein helps preserve muscle mass during weight loss, which is especially important because hypothyroidism can already contribute to muscle weakness. It also keeps you feeling fuller for longer, which is helpful when Mounjaro is reducing your appetite.

Good sources include chicken, turkey, fish, eggs, Greek yoghurt, beans and lentils, and tofu.

Healthy fats from whole foods

Fat is an essential part of a balanced diet and plays a role in hormone production, including thyroid hormones. Include a serving of fat with each meal from sources like olive oil, avocado, nuts, seeds, and oily fish.

Oily fish (salmon, mackerel, sardines) are particularly worth including twice a week. They provide omega-3 fatty acids, which have anti-inflammatory properties, and are also a natural source of iodine and selenium, two minerals your thyroid needs.

Vegetables and fruit

Aim to fill half your plate with vegetables at main meals. They provide fibre, vitamins, and antioxidants that support overall health and energy levels.

If you’ve heard that cruciferous vegetables (broccoli, cauliflower, cabbage, kale) are bad for your thyroid, the evidence doesn’t support avoiding them. You’d need to eat extremely large quantities of raw cruciferous vegetables for them to meaningfully affect thyroid function. Cooking them reduces the relevant compounds further.⁵

Complex carbohydrates

Fibre-rich carbohydrates provide steady energy, which is important when fatigue from hypothyroidism is a daily challenge. They also support gut health and help prevent constipation, which is already common in hypothyroidism.

Choose from wholegrain or sourdough bread, rolled oats, brown rice, potato, sweet potato, quinoa, beans and lentils, wholemeal pasta or noodles, and wholemeal couscous.

Iodine and selenium from food

Your thyroid needs iodine to produce thyroid hormones and selenium to convert them into their active form. Most people in the UK get enough from a varied diet, but it’s worth knowing which foods are good sources.⁵

Iodine is found in fish, shellfish, dairy products, and eggs. Selenium is found in Brazil nuts (just one or two a day provides your daily requirement), fish, meat, and eggs.

Supplementing with high-dose iodine or selenium isn’t recommended unless your doctor has identified a specific deficiency. Too much of either can actually worsen thyroid problems.⁵

Eating 3 balanced meals a day, even if you’re not hungry

Mounjaro significantly reduces appetite, which can make it hard to eat enough nourishing food. This is especially important with hypothyroidism, where under-eating can worsen fatigue and make it harder for your body to produce thyroid hormones.

On low-appetite days, focus on nutrient-dense options that don’t require large portions: Greek yoghurt with berries, scrambled eggs on sourdough, a handful of nuts, or a smoothie with spinach, banana, and protein powder.

Batch cooking on higher-energy days means you’ll have meals ready to reheat when fatigue makes cooking difficult.

Foods to be mindful of

Ultra-processed foods, sugary snacks, and excessive alcohol provide little nutritional value and can worsen the fatigue and brain fog that hypothyroidism already causes.

It’s also worth noting that calcium supplements, iron supplements, and soy products can interfere with levothyroxine absorption if taken too close together. Leave at least four hours between levothyroxine and these.²

Movement and hypothyroidism

Exercise can help counteract several of the symptoms hypothyroidism causes, including fatigue, weight gain, low mood, and muscle weakness. But the fatigue that comes with an underactive thyroid can make even small amounts of activity feel like a huge effort.

The most important thing to know is that any movement is better than none. You don’t need to hit any particular target to benefit.

Building movement into your routine

Research on habit formation shows that it takes an average of 66 days for a new behaviour to become automatic.⁶ The key is starting with something so small it barely feels like effort, and linking it to something you already do.

For example, a 10-minute walk after lunch, or some gentle stretching while the kettle boils. Once that feels natural, gradually do a little more as it feels manageable.

This approach works better than ambitious plans, especially when your energy levels vary day to day with hypothyroidism.

Why resistance training is worth considering

Hypothyroidism can cause muscle weakness and loss of muscle mass over time. Resistance training, whether that’s bodyweight exercises, resistance bands, or light weights, can help counteract this.

You don’t need a gym membership. Bodyweight exercises like squats, wall press-ups, and seated leg raises are effective starting points you can do at home.

Working with your energy levels

Many people with hypothyroidism find their energy levels follow a pattern, often lower in the morning and slightly better in the afternoon. If that’s you, scheduling activity for when you tend to feel best can help.

On days when fatigue is particularly bad, a short walk or five minutes of stretching still counts. Consistency matters more than intensity.

As a general guide, the NHS recommends 150 minutes of moderate activity per week, but this is a long-term aspiration, not a starting point. Begin wherever you are and build up gradually.

Looking after your mental health

Depression and anxiety are significantly more common in people with hypothyroidism than in the general population. Research suggests that around 40-50% of people with hypothyroidism experience depressive symptoms, even when their thyroid levels are adequately treated with levothyroxine.⁵

There are several reasons for this. Thyroid hormones play a direct role in brain chemistry, affecting serotonin and other neurotransmitters involved in mood. The chronic fatigue that comes with hypothyroidism also takes a toll, making everyday tasks feel exhausting and reducing motivation.

The fatigue burden

Fatigue is one of the most common and frustrating symptoms of hypothyroidism. Many people describe it as different from normal tiredness: a deep exhaustion that doesn’t improve with sleep.

When you add Mounjaro’s appetite-reducing effects, it’s important to make sure you’re eating enough. Under-eating can make fatigue significantly worse. Regular, balanced meals (even small ones) help maintain energy throughout the day.

Brain fog and concentration

Many people with hypothyroidism experience cognitive difficulties, sometimes described as ‘thyroid brain fog’. This can include poor concentration, difficulty finding words, and short-term memory problems.

Making sure your levothyroxine dose is optimised is the first step. Beyond that, managing sleep, staying active, and eating regularly can all help. If brain fog persists despite normal thyroid levels, it’s worth discussing with your GP.

When to speak to your GP

If you notice persistent low mood, loss of interest in things you used to enjoy, increased anxiety, or thoughts of self-harm, speak to your GP. Depression is treatable, and getting support early makes a difference.

It’s also worth asking your GP to recheck your thyroid levels if your mood changes noticeably, as this can sometimes indicate that your levothyroxine dose needs adjusting.

Cognitive behavioural therapy (CBT) has good evidence for depression and anxiety in people with long-term health conditions. Your GP can refer you.

Mounjaro clinical data

Frequently asked questions

Can I take Mounjaro if I have Hashimoto’s thyroiditis?

Yes. Hashimoto’s is the most common cause of hypothyroidism in the UK, and having it doesn’t prevent you from taking Mounjaro. The contraindication is specifically for medullary thyroid carcinoma (MTC) and MEN 2, which are different conditions. If you’re unsure, your prescriber can clarify.

Will Mounjaro affect my levothyroxine absorption?

It might, because Mounjaro slows gastric emptying, which can affect how oral medications are absorbed. The best approach is to take your levothyroxine on an empty stomach, 30-60 minutes before food, and at a different time of day from your Mounjaro injection. Regular thyroid blood tests will show if your dose needs adjusting.¹

How often should I get my thyroid levels checked while on Mounjaro?

Every 8-12 weeks during active weight loss is a reasonable approach. Weight loss can change how much levothyroxine your body needs, so more frequent monitoring than the standard annual check is sensible. Ask your GP to add TSH and free T4 to your routine blood tests.

Can Mounjaro cause thyroid problems?

There’s no evidence that Mounjaro causes hypothyroidism or worsens existing hypothyroidism. A 2023 conference abstract actually suggested a small beneficial effect of tirzepatide on TSH levels, though this is preliminary and needs confirming in larger studies.⁴ The MTC contraindication is a precaution based on animal data, not evidence of harm in humans.

I’m always tired from my thyroid condition. Will Mounjaro make it worse?

Mounjaro doesn’t typically cause fatigue. However, eating significantly less than usual can make tiredness worse, which is a real concern when hypothyroidism fatigue is already an issue. Focus on nutrient-dense foods, eat regular meals even when your appetite is low, and stay hydrated. If fatigue worsens, ask your GP to recheck your thyroid levels.

Should I avoid cruciferous vegetables like broccoli and kale?

No. The idea that cruciferous vegetables harm your thyroid is a persistent myth. You’d need to eat extremely large quantities of raw cruciferous vegetables for them to meaningfully affect thyroid function, and cooking reduces the relevant compounds further.⁵ These vegetables are nutritious and shouldn’t be avoided.

Do I need to take iodine or selenium supplements?

Not unless your doctor has identified a specific deficiency. Most people in the UK get enough iodine and selenium from a varied diet that includes fish, dairy, eggs, and nuts. Supplementing with high doses of either mineral can actually worsen thyroid problems, so it’s better to focus on food sources.⁵

Can losing weight on Mounjaro improve my thyroid function?

Weight loss is associated with improvements in TSH levels, particularly in people who had elevated TSH related to excess weight.⁴ However, if you have autoimmune hypothyroidism (Hashimoto’s), weight loss won’t reverse the underlying condition. You’ll likely still need levothyroxine, though your dose may need reducing as you lose weight.

What’s the difference between medullary thyroid cancer and regular thyroid conditions?

Medullary thyroid carcinoma (MTC) is a rare type of thyroid cancer that affects the C-cells of the thyroid. It’s completely different from hypothyroidism, Hashimoto’s, or the more common papillary and follicular thyroid cancers. Having hypothyroidism doesn’t increase your risk of MTC.

Take home message

You can take Mounjaro if you have hypothyroidism. The key practical consideration is timing your levothyroxine carefully, taking it on an empty stomach at a different time of day from your Mounjaro injection, and getting your thyroid levels checked more frequently during weight loss.

Mounjaro is contraindicated in people with a personal or family history of MTC or MEN 2, but these are rare conditions unrelated to standard hypothyroidism or Hashimoto’s.

Alongside medication, eating a balanced diet rich in protein, healthy fats, vegetables, and complex carbohydrates supports both thyroid function and healthy weight loss. Building gentle movement habits and looking after your mental health are equally important, especially given the fatigue and mood changes that hypothyroidism can cause.

Second Nature’s Mounjaro programme combines medication with support from registered dietitians and a structured habit-change programme. It’s built around the balanced plate model (half vegetables, a quarter protein, a quarter complex carbohydrates, plus a serving of fat) and focuses on sustainable changes rather than restrictive dieting.

In a published study, active subscribers on Second Nature’s semaglutide-supported programme lost an average of 19.1% of their body weight at 12 months, with 77.7% achieving at least 10% weight loss.⁷

References

1. Electronic Medicines Compendium. (2024). Mounjaro (tirzepatide) Summary of Product Characteristics.
2. NHS. (2024). Underactive thyroid (hypothyroidism).
3. Aronne, L.J. et al. (2024). Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: the SURMOUNT-4 randomised clinical trial. JAMA, 331(1), 38-48.
4. Yu, G.K. et al. (2023). FRI483 Changes in thyroid function test with tirzepatide use in patients with hypothyroidism [conference abstract]. Journal of the Endocrine Society, 7(Supplement_1), bvad114.1829.
5. British Thyroid Foundation. (2024). Thyroid and diet factsheet.
6. Lally, P. et al. (2010). How are habits formed: modelling habit formation in the real world. European Journal of Social Psychology, 40(6), 998-1009.
7. Richards, R. et al. (2025). A remotely delivered GLP-1RA-supported specialist weight management program in adults living with obesity: retrospective service evaluation. JMIR Formative Research, 9(1), e72577.