Jump to: What is hypothyroidism? | What is Mounjaro? | Medication timing and interactions | Why take Mounjaro if you have hypothyroidism? | Monitoring and safety considerations | Frequently asked questions | Take home message
You can take Mounjaro (tirzepatide) if you have an underactive thyroid (hypothyroidism) and your BMI is over 27. There are no known interactions between Mounjaro and thyroid medications like levothyroxine.
However, hypothyroidism can affect your metabolism and make weight loss more challenging. Your thyroid levels must be well-controlled with medication before starting Mounjaro.
Hypothyroidism affects approximately 2-3% of people in the UK1. While clinical trials show Mounjaro leads to an average weight loss of 20-22.5% at 72 weeks, no studies have specifically examined its effectiveness in people with hypothyroidism.
Theoretically, Mounjaro may help overcome the metabolic challenges of an underactive thyroid by reducing appetite and helping people eat less. However, these potential benefits remain unproven.
Important safety information: Mounjaro (tirzepatide) is a prescription-only medication for treating type 2 diabetes and managing obesity. Always consult with your healthcare provider before starting any new medication, particularly if you have thyroid conditions or take thyroid medications. Mounjaro is contraindicated in patients with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
Can I take Mounjaro? Quick decision guide
✅ Yes, if you have:
- Stable TSH (0.4-4.5 mU/L) for 3+ months
- Regular levothyroxine routine established
- No thyroid cancer history
- BMI ≥27 with comorbidities or ≥30
⚠️ Maybe, talk to a specialist if:
- TSH between 5-10 mU/L
- Recent thyroid medication changes
- Hashimoto’s with fluctuating levels
- Other endocrine conditions
❌ No, if you have:
- Personal/family history of medullary thyroid cancer
- MEN 2 syndrome
- Unstable thyroid levels
- Currently pregnant/breastfeeding
What is hypothyroidism (underactive thyroid)?
Hypothyroidism occurs when the thyroid gland fails to produce enough thyroid hormones (T3 and T4). These hormones are crucial in regulating your metabolism, energy levels, and weight.
Normal TSH levels typically range from 0.4 to 4.5 mU/L. In the UK, hypothyroidism is usually diagnosed when TSH exceeds 10 mU/L, or between 5-10 mU/L with symptoms3.
The most common cause of hypothyroidism is Hashimoto’s disease, an autoimmune disorder where the immune system attacks the thyroid gland. Common symptoms include fatigue, weight gain, cold sensitivity, dry skin, and depression.
Research shows that people with hypothyroidism often have a metabolic rate that’s 10-30% slower than normal4. This reduction can make losing weight more difficult, even with diet and exercise.
The condition is usually treated with levothyroxine, which replaces the missing thyroid hormone. When properly treated, most symptoms improve, including the ability to manage weight more effectively.
What is Mounjaro?
Mounjaro is a dual-action weight-loss injection approved by the MHRA for weight management in the UK. It supports weight loss by mimicking two hormones, GLP-1 and GIP, that communicate with the brain’s appetite control centre, the hypothalamus, to lower hunger and food-seeking behaviour.
By lowering hunger and our desire to eat, Mounjaro helps us eat fewer calories to achieve a calorie deficit. This occurs when we consume fewer calories than our body needs for essential functions.
Mounjaro also slows down the rate at which we digest food, prolonging feelings of fullness. Clinical trials demonstrate average weight loss of 20-22.5% over 72 weeks with the highest dose2.
| Factor |
Without hypothyroidism |
With hypothyroidism |
| Average weight loss |
20-22.5% at 72 weeks2 |
No specific data available |
| Metabolism rate |
Normal |
May be 10-30% slower4 |
| Required monitoring |
Weight, side effects |
Plus TSH every 6-12 weeks initially |
| Medication timing |
Flexible |
Consider thyroid med timing |
| Special considerations |
Standard protocol |
Possible thyroid dose adjustments |
Medication timing and interactions
Understanding how to time your medications is crucial for optimal absorption and effectiveness. Fortunately, there are no known drug interactions between Mounjaro and levothyroxine.
Levothyroxine timing:
- Take on an empty stomach, 30-60 minutes before breakfast
- Alternatively, take at bedtime, 3-4 hours after your last meal
- Consistency is key – take at the same time each day
Mounjaro timing:
- Can be taken at any time of day, with or without food
- Choose a consistent day each week
- Many people prefer mornings for routine consistency
Practical tips:
- Space medications by at least 30 minutes for comfort
- Set reminders for both medications
- Keep a medication diary initially to track timing and any symptoms
Why take Mounjaro if you have hypothyroidism?
GLP-1 medications like Mounjaro may help people with hypothyroidism who struggle with weight management.
However, these potential benefits are theoretical, as no studies have specifically examined Mounjaro’s effectiveness in people with hypothyroidism.
Weight loss can be particularly challenging with hypothyroidism due to a slower metabolic rate.
Mounjaro may help overcome this challenge through different mechanisms than thyroid hormones.
The medication’s ability to reduce appetite and slow digestion works independently of thyroid function. This could help create the sustained calorie deficit needed for weight loss, even with a slower metabolism.
One small study of 17 participants found that tirzepatide can lower thyroid-stimulating hormone (TSH) levels5.
However, the clinical significance of this finding remains unclear, and it’s unknown whether this would affect weight loss outcomes.
Important considerations include:
- People with hypothyroidism may still experience slower weight loss compared to those without the condition
- Losing weight may improve thyroid function and potentially reduce thyroid medication needs
- Any medication adjustments should only be made under medical supervision
Monitoring and safety considerations
Proper monitoring is essential when taking Mounjaro with hypothyroidism. Your healthcare team should establish a clear monitoring schedule before starting treatment.
Baseline requirements:
- TSH should be stable within normal range for at least 3 months
- Recent thyroid function tests (TSH, T4)
- Discussion of thyroid cancer family history
Monitoring schedule:
- TSH levels at baseline
- Recheck at 6 weeks after starting Mounjaro
- Then every 3 months for the first year
- Adjust frequency based on stability
Warning signs to contact your doctor:
- Symptoms of hyperthyroidism: racing heart, anxiety, excessive sweating, tremors
- Symptoms of worsening hypothyroidism: extreme fatigue, severe cold intolerance, depression
- Any neck swelling, lumps, or voice changes
- Unexpected weight changes or plateau despite adherence
Frequently asked questions
Can I take Mounjaro and levothyroxine at the same time?
While there are no direct interactions, it’s best to space them by at least 30 minutes.
Levothyroxine needs to be taken on an empty stomach for optimal absorption, while Mounjaro can be taken with or without food.
What TSH level is safe to start Mounjaro?
Your TSH should generally be within the normal range (0.4-4.5 mU/L) and stable for at least 3 months.
Your doctor may have specific requirements based on your individual situation.
Will I lose weight more slowly than people without thyroid issues?
Possibly. Your metabolism may be 10-30% slower even with treatment, which could affect your rate of weight loss.
However, no specific data exists comparing weight loss on Mounjaro between people with and without hypothyroidism.
How often should I check my thyroid levels on Mounjaro?
Initially, check TSH at baseline, then at 6 weeks, and every 3 months for the first year.
Your doctor may adjust this schedule based on your stability and response.
Can Mounjaro affect my thyroid medication dose needs?
Yes. As you lose weight, your thyroid medication requirements may change. This is why regular monitoring is essential. Never adjust your thyroid medication without medical supervision.
Are there any thyroid conditions where Mounjaro is contraindicated?
Yes. Mounjaro is contraindicated if you have a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
What are the signs my thyroid medication needs adjusting?
Signs of too much thyroid medication include heart palpitations, anxiety, insomnia, and heat intolerance. Signs of too little include fatigue, weight gain, cold intolerance, and depression.
Should I see an endocrinologist before starting?
It’s recommended for those with unstable thyroid levels, a complex thyroid history, or other endocrine conditions. Your GP can advise whether a specialist referral is needed.
Take home message
Mounjaro can be taken safely with hypothyroidism when thyroid levels are well-controlled, but careful monitoring is essential. No studies have specifically examined its effectiveness in people with thyroid conditions.
Success depends on maintaining consistent thyroid treatment while using Mounjaro. Regular monitoring of thyroid levels is crucial, as weight loss may affect your medication needs.
Remember that Mounjaro is contraindicated if you have a history of medullary thyroid carcinoma or MEN 2 syndrome. Always work closely with your healthcare team to ensure safe and effective treatment.
Second Nature's Mounjaro and Wegovy programmes
Second Nature provides Mounjaro or Wegovy as part of our Mounjaro and Wegovy weight-loss programmes.
Why choose Second Nature over other medication providers, assuming you're eligible?
Because peace of mind matters.
We've had the privilege of working with the NHS for over eight years, helping people across the UK take meaningful steps toward a healthier, happier life.
Our programmes are designed to meet people where they are, whether that means support with weight loss through compassionate one-to-one health coaching, or access to the latest weight-loss medications (like Mounjaro and Wegovy) delivered alongside expert care from a multidisciplinary team of doctors, psychologists, dietitians, and personal trainers.
At the heart of everything we do is a simple belief: real, lasting change comes from building better habits, not relying on quick fixes. We're here to support that change every step of the way.
With over a decade of experience, thousands of lives changed, and a long-standing record of delivering programmes used by the NHS, we believe we're the UK's most trusted weight-loss programme.
We hope to offer you something invaluable: peace of mind, and the support you need to take that first step.
References
- National Institute for Health and Care Excellence. (2024). Hypothyroidism: Prevalence. NICE Clinical Knowledge Summaries.
- Jastreboff AM, et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. New England Journal of Medicine. 387(3):205-216.
- National Institute for Health and Care Excellence. (2019). Thyroid disease: assessment and management.
- Biondi B, Wartofsky L. (2014). Treatment with thyroid hormone. Endocrine Reviews. 35(3):433-512.
- Yu GK, Nakhle S, Vernetti NJ, Chao A. (2023). FRI483 Changes In Thyroid Function Test With Tirzepatide Use In Patients With Hypothyroidism. Journal of the Endocrine Society. 7(Supplement_1):bvad114.1829.
- Medicines and Healthcare products Regulatory Agency. (2023). MHRA authorises diabetes drug Mounjaro (tirzepatide) for weight management and weight loss.
- British Thyroid Foundation. (2024). Thyroid disorders: patient information.
