Can you take levothyroxine with Mounjaro (tirzepatide)?
Is it OK to combine levothyroxine with Mounjaro? Discover how these medications can work safely together.
If you rely on levothyroxine to manage an underactive thyroid (hypothyroidism), you already know how critical it is to keep your hormone levels stable.
On top of that, many people with hypothyroidism find that losing weight can feel like a never-ending uphill battle – especially when the scale doesn't budge, no matter how disciplined you are.
At SemaPen, we often see people balancing their need for essential thyroid hormone replacement along with a desire for a more effective way to lose weight.
Below, we explore:
- Whether you can take Mounjaro (tirzepatide) at the same time as levothyroxine
- Why levothyroxine matters for healthy thyroid function
- What current research says about possible interactions between the two drugs
What is levothyroxine?
Levothyroxine is a synthetic version of thyroxine – a hormone your thyroid would ordinarily produce on its own. When the thyroid gland slows down (hypothyroidism), you end up with too little thyroxine in your bloodstream. This can lead to several symptoms, including:
- Fatigue
- Weight gain
- Slow metabolism
- Dry hair and skin
- Low mood
In short, levothyroxine isn't just a 'nice-to-have'. It's often the sole way for many people with hypothyroidism to replace the missing hormone, keep their metabolism steady and boost everyday energy levels.
If that's you, it's understandable why the idea of adding another medication – such as Mounjaro – might raise a few questions.
Can you take Mounjaro and levothyroxine together?
The short answer
Yes – most people can use Mounjaro and levothyroxine at the same time. There's no 'absolutely not' rule that says these two medications can't coexist in the body.
However, they may subtly influence one another – especially when it comes to changes in your blood sugar or body weight. Keeping a close eye on thyroid levels can help you stay on track. And make sure to touch base with your SemaPen team or another healthcare provider if you notice any shifts.
Diving into the science
Deep dive 1: how tirzepatide may affect metabolism
Mounjaro is a dual-action medication that mimics two hormones: GLP-1 (like semaglutide) and GIP. Together, they help:
- Regulate appetite (so you feel full sooner and stay satisfied longer)
- Improve blood sugar control by boosting insulin release when your blood sugar is high
- Slow gastric emptying, which can help curb sudden overeating
Meanwhile, levothyroxine ensures you have enough thyroid hormone to support your metabolism and energy levels.
In other words…
It's like Mounjaro is a friendly messenger telling your body, 'We've eaten enough—no need to keep munching!' Levothyroxine, meanwhile, is another messenger that keeps the energy factory running smoothly.
Having two messengers can sometimes mean they talk over each other, so you should watch them both closely.
Deep dive 2: potential dose adjustments
According to reputable drug-interaction sources, significant weight loss or changed blood sugar control may require a tweak to your levothyroxine dose. Why? Because your body's thyroid hormone needs might shift if you lose a substantial amount of weight.
In other words…
Imagine you've been wearing a thick winter coat for ages, then suddenly move to a warm climate. You'd likely need a lighter coat.
Likewise, if your body composition changes due to Mounjaro, your old levothyroxine 'coat' might be too heavy, so your doctor might adjust it.
Deep dive 3: timing and absorption
Levothyroxine is usually best absorbed in the morning on an empty stomach – ideally at least 30 minutes before breakfast or caffeine.
Because Mounjaro can slow how quickly your stomach empties, some healthcare professionals recommend a time gap between your tirzepatide injection and your levothyroxine dose. If you're unsure, follow your prescriber's guidance.
In other words:
Picture levothyroxine as a sponge that needs time to soak up water. Adding other medications too soon (like Mounjaro) might interfere with absorption. Spreading them out ensures each medication has its moment to do its job.
Key points to keep in mind
- Yes – you can generally take Mounjaro and levothyroxine together.
- Keep tabs on your thyroid function. Substantial weight loss or a notable shift in blood sugar may mean your levothyroxine dose needs a tweak.
- Stay in touch with your healthcare team. Whether it's your GP, an endocrinologist or the SemaPen team, professional input is key for managing both your thyroid and your weight.
Summing up
If you're on levothyroxine to handle your thyroid and want to explore Mounjaro injections for weight loss, know that these two meds typically play nicely together.
Just make sure to keep your healthcare provider in the loop – especially if you spot changes in energy levels, mood or weight.
Here at SemaPen, we understand that good thyroid function and successful weight management often go hand in hand, and we're here to support you every step of the way.
Sources
https://www.nhs.uk/medicines/levothyroxine
https://www.drugs.com/drug-interactions/levothyroxine-with-mounjaro-1463-0-4363-20051.html
https://medical.lilly.com/us/products/answers/can-people-take-mounjaro-tirzepatide-with-levothyroxine-199579
This article was reviewed by and approved by Alice Fletcher, Lead Bariatric Dietitian, on 3 April 2025.
