Jump to: What is levothyroxine? | What is Mounjaro? | Why would you take Mounjaro alongside levothyroxine? | Take home message
You can take Mounjaro with levothyroxine (also known as L-thyroxine), but there are possible interactions between the medications, so caution is advised.
While on Mounjaro and levothyroxine, you must remain in close communication with your local healthcare team and prescribing pharmacists to monitor your body’s response to the medications.
People living with an underactive thyroid have a greater risk of developing obesity, so the combination of Mounjaro and levothyroxine may support weight loss and help regulate metabolism.
What is levothyroxine (L-thyroxine)?
Levothyroxine is a drug that mimics the naturally occurring thyroid hormone T4. It’s prescribed for people living with an underactive thyroid to help regulate metabolism, core body temperature, and energy levels.
Levothyroxine is an oral medication and is typically taken once daily on an empty stomach.
The thyroid gland is an organ at the front of your neck. The primary function of the thyroid gland is to produce and release two hormones:
- Thyroxine (T4)
- Triiodothyronine (T3)
These two hormones regulate our metabolism, energy levels, and core body temperature.
People living with an underactive thyroid struggle to produce and release these hormones and are prescribed synthetic versions of them to help maintain normal metabolism, energy levels, and core body temperature.
As T4 and T3 help to regulate our metabolism, people living with an underactive thyroid may be more likely to develop obesity.
Observational research suggests people living with underactive thyroid (hypothyroidism) have an 86% higher relative risk of developing obesity compared to those not living with the condition.
This increased risk of developing obesity for those living with hypothyroidism is one reason why you may also be prescribed Mounjaro alongside levothyroxine.
What is Mounjaro?
Mounjaro is a dual-action weight-loss injection that mimics two hormones in the body that help us feel fuller and lose weight.
The drug in Mounjaro is tirzepatide, which is a synthetic mimic of GLP-1 and GIP. GLP-1 and GIP are hormones released by the gut after we eat to help us feel full and manage our blood sugar levels.
Mounjaro is a long-acting medication injected once a week. It takes 4-5 weeks for the drug to reach a steady state in the body, where the levels in the blood remain consistent and the drug’s effects become more pronounced.
Research suggests Mounjaro supports weight loss of up to 26% after two years, which is around 10% more weight loss than another well-known weight-loss injection, Wegovy.
Why would you take Mounjaro alongside levothyroxine?
If you’re living with hypothyroidism (underactive thyroid) and also obesity and have struggled to lose weight and keep it off in the past, you may consider taking Mounjaro alongside levothyroxine.
While levothyroxine is a hormone replacement therapy to help recover some of the loss of function of the thyroid gland, it may not be a sufficient boost to your metabolism to aid weight loss in the long term.
Mounjaro could enable you to eat at a calorie deficit for a sustained period to support weight loss in the long term.
Here’s a list of things to consider when taking levothyroxine with Mounjaro:
- You should consult your GP or pharmacist before taking Mounjaro with levothyroxine
- Your GP should monitor your thyroid parameters regularly when taking both medications
- Your levothyroxine dose may change if you lose weight on Mounjaro, as losing body fat can alter your metabolism. Your GP will monitor this and react accordingly.
- Be mindful of side effects as you increase your dose of Mounjaro and report your side effects to your GP or prescribing pharmacist so they can continue to monitor your progress
However, there isn’t currently any research investigating the combination of Mounjaro with levothyroxine, and it’s possible some individuals will experience adverse effects from taking these drugs simultaneously.
If you’re signing up for Second Nature’s Mounjaro programme, the clinical team will discuss and confirm this, but in general, if you’re taking levothyroxine, you will be able to take Mounjaro.
If you do start taking levothyroxine with Mounjaro, we recommend letting your GP or local pharmacist know.
Take home message
There’s potential for levothyroxine and Mounjaro to play a complementary role in supporting people living with obesity and underactive thyroid to achieve lasting weight loss.
Most people taking levothyroxine will be eligible for Mounjaro, but if you do start taking Mounjaro then it’ll be very important to let your GP know so they’re aware and can monitor your progress and adjust any future levothyroxine doses, if needed.
Second Nature has launched a Mounjaro weight-loss programme aimed at helping people develop the healthy habits they need to lose weight and keep it off in the long term.
If you’d like to see if you’re eligible for our Mounjaro programme, click here to take your health quiz.
