Mounjaro and levothyroxine

Are Mounjaro and levothyroxine safe to take together? If you have an underactive thyroid gland and struggle with weight management, you might wonder if you can take Mounjaro with levothyroxine.

While these medications can generally be taken together, it’s essential to understand how they interact to make sure that you are not causing more harm than good. Here’s everything you need to know about Mounjaro and levothyroxine.

Thyroid levels and body weight

Since thyroid hormones are responsible for our metabolism, there is a perception that we tend to gain weight when their levels are low. How many times have we blamed our weight gain on our metabolism? Before we look at Mounjaro and levothyroxine in more detail, let’s first review how our thyroid hormones are related to our weight.

The role of thyroid hormones in metabolism and body weight

Thyroid hormones are critical for managing your body’s growth, development, and energy use. Let’s look at how they achieve this:

Thyroid hormones and metabolism

Thyroid hormones control your basal metabolic rate (BMR)—the energy your body uses at rest. This directly affects how many calories you burn daily, even without physical activity (Rosenbaum, M et al., 2000). So, if your metabolism is sluggish, then unfortunately, you will tend to gain the pounds.

Thyroid hormones and temperature regulation

They also influence thermogenesis, the process by which your body generates heat, helping to maintain body temperature (Iwen K.A.et al., 2018). So, if everyone around you is sporting T-shirts and shorts and you are wrapped up in layers of thick jumpers, it may be down to your thyroid levels. Alternatively, maybe you are just friends with some very cold-tolerant people who like ice baths and cold showers.

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Thyroid hormones glucose and fat metabolism

These hormones are vital for lipid metabolism, including breaking down fats for energy and regulating cholesterol levels (Pucci E et al., 2000).

They also play a role in glucose metabolism, ensuring stable blood sugar levels (Pucci E et al., 2000).

Also, by controlling fat oxidation, thyroid hormones help determine how efficiently your body burns fat as fuel (Pucci E et al., 2000).

So, now you are probably getting a better understanding of why people tend to gain weight when these vital hormones are low.

Euthyroid a balance

Eu what? Euthyroid refers to a state where the thyroid gland is functioning normally, producing the right amount of thyroid hormones (T3 and T4) needed for the body to maintain a healthy metabolism.

In a euthyroid state, thyroid hormone levels are neither too high (as in hyperthyroidism) nor too low (as in hypothyroidism). It’s the thyroid level that Goldilocks would choose. This balance is crucial for overall health, as thyroid hormones regulate essential functions like energy production, metabolism, and body temperature.

However, what happens when you slip out of this euthyroid state? Or, to stretch the Goldilocks metaphor further, what happens when your porridge is too hot or cold?

Hyperthyroidism or excess thyroid hormone

When your thyroid produces too much hormone, it creates a hypermetabolic state (Motomura, K. et al., 1998):

• Weight loss: Your body burns energy faster than normal.
• Low cholesterol: Cholesterol levels drop as the body uses fats more efficiently.
• Increased fat breakdown: The body breaks down fat stores (lipolysis).
• Higher glucose production: Your liver produces more glucose for energy (gluconeogenesis).

I know what you are thinking, and before you ask, the answer is NO! You should NEVER take levothyroxine to lose weight. It could result in a thyroid storm, which can be fatal, and if you are not convinced, you can read the following case study:

Lethal thyroid storm after uncontrolled intake of liothyronine in order to lose weight

Hypothyroidism (Too little thyroid hormone)

What happens if you flip the thyroid switch the other way? With low thyroid hormone levels, your metabolism slows, leading to (Melmed S et al., 2015):

• Weight gain: Your body burns less energy, storing more as fat.
• Higher cholesterol: Fat processing slows down, increasing cholesterol levels.
• Reduced fat breakdown: The body struggles to use stored fat.
• Lower glucose production: Your liver produces less glucose.

How thyroid hormones balance energy

Thyroid hormones work like a thermostat for energy use, controlling the balance between energy storage and energy expenditure  (Iwen, K.A et al., 2013). So, just like you want your house to be energy efficient, especially when the prices for gas and electricity are practically extortionate, your thyroid hormones ensure your body is primed for maximum energy efficiency.

What is levothyroxine?

OK, so you have been diagnosed with low thyroid levels, so what do you do? Do you resign yourself to a life of constant weariness and weight gain? Well, thanks to science, we can replace our T4 thyroid hormones. Yes, there is also a T3, but we won’t go into that in this blog; it’s a bit controversial, so it will get its own blog; stay tuned.  

Levothyroxine, also known as L-thyroxine, is a synthetic form of T4, a hormone produced by the thyroid gland. This medication helps manage metabolism, body temperature, and energy levels in people with an underactive thyroid. Taking levothyroxine daily, usually on an empty stomach, helps replace the body’s natural T4 levels, keeping your metabolism and energy steady (Almandoz, J.P. et al., 2012).

Mounjaro and levothyroxine

So now we should know that people with hypothyroidism may have a harder time with weight management due to their slower metabolism. Research shows that those with underactive thyroids are at higher risk of developing obesity (Biondi, B., 2023).

For some, adding a medication like Mounjaro to their levothyroxine treatment may help boost their weight loss efforts. But can you take Mounjaro with levothyroxine? Are there any interactions? Before we find out, let’s turn our attention to Mounjaro.

What is Mounjaro?

Mounjaro, the brand name for tirzepatide, is a newly approved weekly injection for weight loss. In November 2023, the UK’s Medicines and Healthcare Products Regulatory Agency (MHRA) licensed Mounjaro for use in adults with obesity (a BMI of 30 or above) or those who are overweight (a BMI between 27 and 30) and have health conditions related to their weight (MHRA 2023).

Mounjaro is an injectable medication that supports weight loss and blood sugar control. It mimics two hormones—GLP-1 and GIP—that help regulate blood glucose levels and make you feel full after meals. It’s a weekly injection, making it super convenient to use, and because it’s a subcutaneous injection, it’s not that painful to administer.

Mounjaro has shown significant results for weight loss. The  Surmount 1 trial, carried out over 72 weeks, saw individuals lose up to 22.5% of their body weight when taking the Mounjaro 15mg injection. The Surmount 4 trial, which researched weight loss in severely obese individuals (those with a BMI ?35 kg/m²), saw a massive 24.2% weight loss in those individuals who used the Mounjaro 15mg.

To learn more about Mounjaro, why not read our blog, “What is Mounjaro?”

What strengths of Mounjaro are available?

Mounjaro is offered in pre-filled injection pens with the following doses:

Mounjaro 2.5mg, Mounjaro 5mg, Mounjaro 7.5mg, Mounjaro 10mg, Mounjaro 12.5mg, and Mounjaro 15mg. It is administered weekly as a subcutaneous injection, typically in the stomach, thigh, or upper arm.

The dosing schedule for Mounjaro

• Initial Phase: Begin with Mounjaro 2.5mg dose once a week for the first four weeks.
• Dose Increase: Increase to Mounjaro 5mg weekly after the initial phase.
• Further Adjustments: If your healthcare provider recommends, the dose may be gradually increased in four-week intervals, up to a maximum of Mounjaro15mg weekly.

This gradual dose escalation helps the body adjust to the medication and minimises side effects. Clinical trials have shown that most side effects occurred during this adjustment period as the body gets used to Mounjaro (Jastreboff et al., 2022).

How does Mounjaro cause weight loss?

Mounjaro’s active ingredient, tirzepatide, works by controlling appetite, helping you feel full, reducing hunger, and curbing food cravings (MHRA, 2023). This makes it easier to eat less and lose weight naturally.

What sets Mounjaro apart is that it’s the first medication to combine two gut hormones: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). These hormones are called “incretins” because they increase insulin release in response to food in the gastrointestinal tract. Together, they enhance appetite control and metabolism.

Because Mounjaro combines GLP-1 and GIP, it’s often called a “twincretin.” This combination not only suppresses appetite and slows stomach emptying but also enhances the weight-loss effects compared to using just one of these hormones on its own (Coskun T et al., 2018).

In short, Mounjaro’s dual action helps you eat less, stay satisfied longer, and lose more weight effectively.

The following table highlights the benefits of the individual incretins, GLP-1 and GIP.

Comparison between effects of GLP-1 and GIP

Can you take Mounjaro with levothyroxine?

There are no interactions listed between Mounjaro and levothyroxine. Given that being hypothyroid or having lower levels of thyroxine encourages weight gain, it would seem that taking Mounjaro would make sense to help you lose weight. However, just because there are no listed interactions between Mounjaro and levothyroxine, it doesn’t mean that you should not exercise precautions, as the following case study demonstrates.

A case study of increased thyroid levels after taking semaglutide

A case study in the Journal of the American Pharmacists Association highlights the need to closely monitor thyroid hormone levels when taking Mounjaro or a GLP-1 receptor agonist, such as Wegovy.

The case study concerned a 43-year-old woman who had her thyroid removed and was taking levothyroxine for hypothyroidism. After starting a weekly GLP-1 injection, semaglutide, she experienced significantly suppressed thyroid-stimulating hormone (TSH). This change required her levothyroxine dose to be reduced by 25%.

Does semaglutide decrease TSH levels?

The exact mechanism behind the patient’s fall in TSH levels is not fully understood, but may be due to:

• A direct effect of GLP-1 on TSH levels.
• Delayed stomach emptying caused by the medication, which could alter levothyroxine absorption.
• Weight loss associated with GLP-1 use (a 13 kg loss in this case), which may reduce the need for thyroid hormone replacement.

Other studies found a similar effect of TSH when GLP-1 receptor agonists were taken (M.E. Sencar et al 2019, C. Hauge et al 2021).

Why should you be careful before taking Mounjaro with levothyroxine

The above case study demonstrates that GLP-1-containing medications, like Mounjaro,  can impact other treatments, especially those with precise dosing, like levothyroxine.

What does this mean if you are taking levothyroxine for hypothyroidism? Can you still take Mounjaro? Yes, you can take the Mounjaro with levothyroxine, but you should have your thyroid levels checked more frequently.

Mounjaro and levothyroxine summary

This case suggests that weight loss or changes in medication absorption could require adjustments in other prescriptions, emphasising the importance of personalised care. This is why you can always contact us at Medical Mojo for a FREE consultation if you are unsure about taking Mounjaro with levothyroxine or any other medication you may be taking.

If you want to learn more about Mounjaro and other potential interactions, such as can you drink alcohol while taking Mounjaro, check out evidence-based blogs.

How food and timing affect thyroid medication

It’s not just medicines that can interact with levothyroxine, but certain foods and the timing of your meals can impact how well your body absorbs T4 thyroid hormone (levothyroxine).

Certain foods and drinks can reduce how well your body absorbs levothyroxine. Substances like soy products (Conrad S et al., 2004,)  (Fruzza A. et al., 2012 ), papaya (Deiana L et al., 2012), grapefruit (Lilja J et al., 2004), and even coffee (Benvenga S et al., 2008) have been shown to interfere with its absorption, meaning the medication may not work as effectively.

How to take levothyroxine?

The best time to take levothyroxine for improved absorption is on an empty stomach. The best practice is to take your thyroid medication as a single daily dose. Ideally, take it 30–60 minutes before breakfast or at least several hours after eating.

Stick to a consistent routine—take it at the same time every day in the same way (e.g., with or without food). Avoid foods that interfere with absorption close to your dosing time.

These tips can help stabilise your thyroid hormone levels and ensure the medication works effectively.

Is Mounjaro right for you?

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Achieve weight loss with Mounjaro and coaching support

A recent study revealed that adding personalised telephone coaching to an online weight loss program significantly boosted results. Participants who received coaching lost more weight compared to those who didn’t, and the longer the coaching, the better the results over a year. Coaching also helped participants stay on track by encouraging them to monitor progress, use available resources, and stay focused on their goals (Unick JL et al., 2024).

Medical Mojo’s all-in-one weight loss program

At Medical Mojo, we provide a complete weight loss solution with personalised coaching tailored to your needs. Our program includes:

• Weekly one-on-one calls to review your progress.
• Expert advice to set achievable goals.
• Tailored guidance to optimise your weight loss results.

Mounjaro weight loss – simplified

With Medical Mojo, your weight loss journey is fully supported. We provide an entire range of Mounjaro pens and offer coaching to help you get the most out of your treatment. We also include FREE needles and sharps bins to make starting more effortless and less of a faff.

Our program is designed to inspire and empower you, making sustainable weight loss achievable. Let Medical Mojo guide you toward the results you deserve. Begin your journey with us today!

Note: This information is for educational purposes only and should not substitute for professional medical advice.

References

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2. Benvenga S, Bartolone L, Pappalardo M. et al. Altered intestinal absorption of L-thyroxine caused by coffee. Thyroid. 2008;18(3):293–301. 
3. Biondi, B., (2023). Subclinical hypothyroidism in patients with obesity and metabolic syndrome: a narrative review. Nutrients, 16(1), 87.
4. Brent GA. Clinical practice. Graves’ disease. N Engl J Med 358: 2594–2605, 2008.
5. Conrad S, Chiu H, Silverman B. Soy formula complicates management of congenital hypothyroidism. Arch Dis Child. 2004;89(1):37–40. doi: 10.1136/adc.2002.009365. 
6. Deiana, L., Marini, S. and Mariotti, S., 2012. Ingestion of large amounts of papaya fruit and impaired effectiveness of levothyroxine therapy. Endocrine Practice, 18(1), p.98.
7. Fruzza, A.G., Demeterco-Berggren, C. and Jones, K.L., 2012. Unawareness of the effects of soy intake on the management of congenital hypothyroidism. Pediatrics, 130(3), pp.e699-e702.
8. Hartung B, Schott M, Daldrup T, Ritz-Timme S (2010). Lethal thyroid storm after uncontrolled intake of liothyronine in order to lose weight. Int J Legal Med 124(6):637–640
9. C. Hauge, A. Breitschaft, M.L. Hartoft-Nielsen, et al.Effect of oral semaglutide on the pharmacokinetics of thyroxine after dosing of levothyroxine and the influence of coadministered tablets on the pharmacokinetics of oral semaglutide in healthy subjects: an open-label, one-sequence crossover, single-centre, multiple-dose, two-part trial. Expert Opin Drug Metab Toxicol, 17 (9) (2021), pp. 1139-1148
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12. Lilja J, Laitinen K, Neuvonen P. Effects of grapefruit juice on the absorption of levothyroxine. Br J Clin Pharmacol. 2004;60(3):337–41
13. Melmed, S., Polonsky, K.S., Larsen, P.R. and Kronenberg, H.M., 2015. Williams textbook of endocrinology E-Book. Elsevier Health Sciences.
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16. Rosenbaum, M., Hirsch, J., Murphy, E. and Leibel, R.L., 2000. Effects of changes in body weight on carbohydrate metabolism, catecholamine excretion, and thyroid function. The American Journal of clinical nutrition, 71(6), pp.1421-1432.
17. M.E. Sencar, D. Sakiz, M. Calapkulu, et al.The effect of exenatide on thyroid-stimulating hormone and thyroid volume.Eur Thyroid J, 8 (6) (2019), pp. 307-311
18. Unick JL, Pellegrini CA, Dunsiger SI, et al. An Adaptive Telephone Coaching Intervention for Patients in an Online Weight Loss Program: A Randomized Clinical Trial. JAMA Netw Open. 2024;7(6):e2414587. doi:10.1001/jamanetworkopen.2024.14587
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