Taking Mounjaro and Levothyroxine Together: What You Should Know

Levothyroxine is a synthetic thyroid hormone taken by people with hypothyroidism (an underactive thyroid). It is typically taken on an empty stomach, often first thing in the morning, because absorption is sensitive to food, drink, and other medicines taken at the same time.

Mounjaro works partly by slowing gastric emptying — the rate at which the stomach moves food and other substances into the small intestine. This effect is commonly reported, particularly in the early weeks of treatment. Because levothyroxine absorption can be affected by changes in gut motility, some people taking both medicines may find their thyroid hormone levels shift during tirzepatide treatment, even if their levothyroxine dose had previously been stable.

What this means in practice

• Your prescriber or doctor may want to monitor thyroid function (TSH levels) more closely after you start or titrate Mounjaro.
• Levothyroxine is generally taken well before food — your prescriber may advise on the best timing in the context of your weekly injection schedule, but any timing or dose changes are decisions for them, not something to adjust on your own.
• Symptoms such as unusual fatigue, feeling colder than usual, unexpected weight changes, or mood shifts are worth logging and raising with your healthcare team, as they can sometimes reflect changes in thyroid hormone levels.

If you are also on Wegovy (semaglutide), a GLP-1 receptor agonist, a similar consideration applies — the same gastric-emptying effect has been observed with semaglutide, so the question of taking a GLP-1 medicine with levothyroxine is relevant whichever medicine you have been prescribed.

It is also worth knowing that people with thyroid conditions are sometimes interested in whether thyroid dysfunction itself is contributing to weight, and whether medicines like levothyroxine at doses such as 25 mcg affect weight on their own. In general, levothyroxine at any dose is prescribed to correct a hormone deficiency, not as a weight-loss medicine — weight changes from thyroid correction are a secondary effect of restoring normal thyroid function, not a direct treatment for obesity. Your prescriber is the right person to discuss how your thyroid health and weight management interact.

For broader context on Mounjaro, including how it works and commonly reported experiences, see our Mounjaro overview. You may also find it helpful to read about Mounjaro and other hormonal health conditions, or about other medicines people commonly ask about alongside Mounjaro.

When you are managing two medicines simultaneously, spotting patterns in how you feel over time becomes genuinely useful — and that is where GLP Trackr's side-effect and wellbeing tracking is most valuable here.

The app lets you log daily how you feel: energy levels, mood, sleep, and specific symptoms like fatigue or unusual cold sensitivity. Over days and weeks, those logs build into a picture you can bring to your prescriber — far more informative than trying to recall how you felt three weeks ago during a brief appointment. If your thyroid monitoring results prompt a conversation about levothyroxine dose adjustment, having a detailed record of your wellbeing during that period gives your healthcare team much better context.

GLP Trackr also logs each Mounjaro injection — date, dose strength, and site — so you and your prescriber can see exactly where you are in your treatment at any point. The app's built-in doctor report feature can help you present this information clearly at appointments.

Any decision about your levothyroxine dose, your Mounjaro schedule, or any change to either medicine belongs with your prescriber or doctor — they know your thyroid history and full health picture. GLP Trackr supports you in recording and understanding your experience; it is not a substitute for clinical advice. If you notice symptoms that feel severe, persistent, or out of the ordinary, contact your healthcare professional promptly rather than waiting for a routine appointment. Any side effects worth reporting can be passed on through your national reporting scheme (such as the UK's Yellow Card scheme) as well as to your prescriber.

Ready to build a clearer picture of your journey? Download GLP Trackr on the App Store or Google Play and explore it free for 7 days.