Understanding both medications
Before exploring how these medications work together, it’s important to understand what each one does and how they affect your body.
What is levothyroxine?
Levothyroxine is a synthetic version of thyroxine (T4), a hormone naturally produced by your thyroid gland. It’s prescribed to treat an underactive thyroid (hypothyroidism) when your body doesn’t produce enough thyroid hormone naturally.
Levothyroxine works by replacing the thyroid hormone that your body is unable to produce. This helps regulate your metabolism, energy levels, and body temperature.
Key facts about levothyroxine:
- Usually taken as a daily tablet, typically on an empty stomach
- Dosage is highly individualised and based on blood test results
- Full effects may take several weeks to develop
- Requires lifelong treatment for most people with hypothyroidism
- Regular monitoring via blood tests ensures optimal dosing
Thyroid hormones play crucial roles in regulating metabolism, which is why people with untreated hypothyroidism often experience weight gain, fatigue, and feeling cold.
What is Wegovy?
Wegovy (semaglutide) is a once-weekly injectable medication approved for weight management. It belongs to a class of medications called GLP-1 receptor agonists that work by mimicking the action of the GLP-1 hormone in your body.
Wegovy is recommended for weight management in adults with a BMI of at least 35 kg/m² (or 30 kg/m² with weight-related complications) alongside a reduced-calorie diet and increased physical activity.
Key facts about Wegovy:
- Self-administered as a weekly subcutaneous injection
- Starts at a low dose (0.25mg) and gradually increases to reduce side effects
- Works by reducing appetite and slowing gastric emptying
- Clinical trials show an average weight loss of 15-17% after 68 weeks
- Common side effects include nausea, diarrhoea, and constipation
Key points:
- Levothyroxine replaces thyroid hormone that regulates metabolism
- Wegovy reduces appetite and food intake to support weight loss
- Both medications affect metabolism through different mechanisms
- Each medication requires specific timing and administration considerations
Safety and interactions between Wegovy and levothyroxine
Research has identified specific interactions between these medications that require careful consideration and monitoring.
Research evidence on combined use
Research has examined potential interactions between semaglutide and levothyroxine. A comprehensive study published in Expert Opinion on Drug Metabolism & Toxicology found interactions on the combination of these drugs:
- Co-administration of oral semaglutide with levothyroxine resulted in a 33% increase in total thyroxine (T4) exposure compared to levothyroxine alone
- The peak concentration (Cmax) of levothyroxine was not significantly affected
- This interaction is believed to occur because semaglutide delays gastric emptying, which affects levothyroxine absorption
Despite this interaction, the researchers concluded that the combination doesn’t require a change in standard clinical practice.
However, they emphasised the importance of close monitoring of thyroid parameters for patients taking both medications, as levothyroxine dosing may need adjustment.
How the medications affect each other
| Aspect |
Levothyroxine fffect |
Wegovy fffect |
Combined effect |
| Absorption |
Absorbed in the small intestine |
Slows gastric emptying |
Increased total thyroxine exposure by 33%, requiring careful monitoring |
| Metabolism |
Increases metabolic rate |
May decrease caloric intake |
Complementary effects on weight management |
| Blood sugar |
May affect insulin sensitivity |
Improves blood sugar control |
Generally beneficial for those with both thyroid issues and prediabetes |
| Side effects |
Rarely causes gastrointestinal issues |
Commonly causes gastrointestinal side effects |
Monitor for potentially increased digestive symptoms |
NHS and NICE guidance
While neither the NHS levothyroxine information nor NICE guidelines for Wegovy specifically address this combination, both sources emphasise the importance of disclosing all medications to healthcare providers.
The NHS advises patients on levothyroxine to inform their doctor or pharmacist about all medications they’re taking to avoid potentially harmful interactions.
Similarly, NICE guidance for Wegovy recommends comprehensive medical assessment before starting treatment.
Key points:
- Research shows semaglutide increases thyroxine exposure by 33% when taken together
- This interaction doesn’t prevent combined use but requires careful monitoring
- More frequent thyroid function testing is recommended (every 3-6 months)
- Both medications should be disclosed to all healthcare providers
Practical guidance for taking Wegovy with levothyroxine
If you’re taking both medications, following specific guidelines can help maximise effectiveness and minimise potential issues.
Timing considerations
The timing of these medications is important, particularly for levothyroxine absorption:
- Levothyroxine: Take first thing in the morning, at least 30-60 minutes before eating or drinking anything other than water, as recommended by the NHS
- Wegovy: Can be administered any time of day, with or without food, on the same day each week
- Separation: Ideally take levothyroxine on a different day to Wegovy
Monitoring recommendations
Regular monitoring is essential when taking both medications, particularly given the known 33% increase in thyroxine exposure:
- Thyroid function tests: While the NICE guidelines for thyroid disease management recommend annual testing for stable patients, more frequent monitoring (every 3 months initially, then every 3-6 months) is advisable when taking Wegovy with levothyroxine
- Watch for hyperthyroidism signs: The increased thyroxine exposure could potentially lead to symptoms of excess thyroid hormone in some patients
- Weight tracking: Monitor and record your weight weekly
- Symptom journal: Track any symptoms that might indicate thyroid hormone levels need adjustment
Signs that your levothyroxine dose may need adjustment:
- Unusual fatigue or energy changes
- Significant hair loss beyond what’s expected with weight loss
- Changes in cold tolerance
- Heart palpitations or increased heart rate
- Sleep disturbances
- Anxiety or nervousness (possible signs of excess thyroid hormone)
- Tremors or shakiness
Communication with healthcare providers
Effective communication with your healthcare team is crucial:
- Inform all healthcare providers about both medications
- Share your weight loss progress with your GP or endocrinologist
- Report any new or worsening symptoms promptly
- Discuss any plans to stop either medication before doing so
- Consider asking for a medication review if you lose more than 5-10% of your body weight
Key points:
- Take levothyroxine first thing in the morning, at least 30-60 minutes before food
- Monitor thyroid function every 3 months initially, then every 3-6 months
- Watch for signs of both under- and over-treatment with thyroid hormone
- Keep all healthcare providers informed about both medications
Special considerations for hypothyroidism and weight loss
The relationship between hypothyroidism, weight management, and Wegovy involves several important considerations.
Hypothyroidism and obesity connection
Research has established important links between thyroid function and weight:
- According to a large population study, people with obesity have approximately an 86% higher relative risk of developing hypothyroidism
- Even when treated with levothyroxine, some patients continue to struggle with weight management
- Thyroid hormones play a key role in regulating our metabolism and energy expenditure
This connection explains why many people with hypothyroidism may benefit from additional weight management support, such as Wegovy.
How weight loss affects thyroid function
Significant weight loss can alter thyroid hormone requirements:
- Research suggests that levothyroxine needs decrease with weight loss; exact dose changes depend on the individual and their needs
- Changes in body composition affect thyroid hormone metabolism and distribution
- Weight loss may improve thyroid hormone sensitivity in some tissues
For these reasons, your levothyroxine dose may need adjustment as you lose weight on Wegovy. This is a positive sign that your body is responding to the weight loss, but requires medical supervision.
Potential benefits of combined therapy
Using Wegovy alongside properly dosed levothyroxine may offer several advantages:
- Complementary effects on metabolism and energy regulation
- Potential for improved quality of life through better weight loss
- Possible reduction in weight-related complications
- Addressing both the metabolic impact of hypothyroidism and the behavioural aspects of eating
NHS pathway considerations
The NHS approach to these conditions involves several aspects:
- Hypothyroidism is typically managed in primary care by GPs
- Access to Wegovy through the NHS is currently limited to specialist weight management services
- Patients may need to discuss both conditions with different healthcare teams
- Private prescriptions for Wegovy are available but require coordination with NHS care for hypothyroidism
Key points:
- Hypothyroidism significantly increases obesity risk, even with treatment
- Significant weight loss may reduce levothyroxine requirements
- Combined therapy addresses both metabolic and appetite regulation
- NHS pathways may involve both primary care and specialist services
Frequently asked questions
Will Wegovy affect my thyroid medication absorption?
Yes, research shows that semaglutide increases total thyroxine (T4) exposure by approximately 33%. This occurs because Wegovy slows gastric emptying, which affects how levothyroxine is absorbed.
To minimise this impact, take levothyroxine first thing in the morning on an empty stomach, and separate it from your Wegovy injection by taking it on a different day. More frequent monitoring of thyroid function is recommended when taking both medications.
How long after taking levothyroxine can I take Wegovy?
It’s best to separate these medications by at least several hours. Take levothyroxine first thing in the morning as recommended by the NHS, then administer Wegovy later in the day, or another day of the week.
Since Wegovy is a weekly injection, you can choose an injection day and time that allows for appropriate separation from your morning levothyroxine.
Do I need different thyroid tests while on Wegovy?
You don’t need different tests, but you do need more frequent monitoring. The standard thyroid function tests (TSH, sometimes T4) remain appropriate.
When taking both medications, more frequent testing (every 3 months initially, then every 3-6 months) is advisable due to the known interaction between semaglutide and levothyroxine, as well as the effects of weight loss on thyroid hormone requirements.
Can Wegovy cause thyroid problems?
There is no evidence that Wegovy causes thyroid dysfunction. Clinical trials of semaglutide (the active ingredient in Wegovy) have not shown significant effects on thyroid function in people with normal thyroid glands.
However, if you’re taking levothyroxine, the combination with Wegovy increases thyroxine exposure by 33%, which requires careful monitoring. Additionally, weight loss from any cause, including Wegovy, may affect your thyroid hormone requirements.
Should I adjust my levothyroxine dose myself if I lose weight on Wegovy?
No, never adjust your levothyroxine dose without medical supervision. If you’re losing weight on Wegovy, schedule thyroid function tests with your GP. Only change your dosage based on test results and your doctor’s recommendation.
Self-adjusting thyroid medication can lead to serious health problems, including both under- and over-treatment of hypothyroidism.
Is it safe to lose weight quickly with hypothyroidism?
Moderate, gradual weight loss is generally safe for people with well-controlled hypothyroidism. However, very rapid weight loss isn’t recommended for various health reasons beyond the impact on levothyroxine medication.
Wegovy typically produces gradual weight loss over months, which is appropriate for everyone, not just people with hypothyroidism. Always keep your healthcare provider informed about your weight changes and any new symptoms.
Can I take both medications long-term?
Yes, both medications can be taken long-term under proper medical supervision. Levothyroxine is typically a lifelong treatment for hypothyroidism.
Wegovy is approved for long-term use in weight management, though decisions about duration should be made with your healthcare provider based on your individual response and needs.
Take home message
You can take Wegovy alongside levothyroxine, but research shows that semaglutide increases thyroxine exposure by 33%, requiring careful monitoring. This combination may be particularly beneficial if you have hypothyroidism and are struggling with weight management despite appropriate thyroid hormone replacement.
Regular thyroid function tests are essential, particularly during active weight loss, as your levothyroxine requirements may change as you lose weight.
To optimise the effectiveness of both medications:
- Take levothyroxine first thing in the morning, at least 30-60 minutes before food
- Administer Wegovy on the same day each week, separated from your levothyroxine dose
- Schedule thyroid function tests every 3 months initially, then every 3-6 months
- Monitor and record your weight and any symptoms regularly
- Inform all healthcare providers about both medications
By following these guidelines and working closely with your healthcare team, you can effectively manage both your thyroid condition and weight, potentially improving your overall health and quality of life.
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.
