Should You Start a GLP-1 Before or After Treating Hypothyroidism?

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‍GLP-1 receptor agonists like semaglutide (Ozempic, Wegovy), liraglutide (Saxenda, Victoza), and tirzepatide (Mounjaro, Zepbound) are making headlines—and for good reason. These powerful medications, first developed to treat type 2 diabetes, are now widely used for weight loss, blood sugar control, and improving overall metabolic health. They’ve even earned FDA approval for obesity treatment and are increasingly being prescribed for conditions like metabolic syndrome, prediabetes, and weight management.

But what if you’re also dealing with thyroid issues—especially hypothyroidism or Hashimoto’s thyroiditis? Is jumping into a GLP-1 medication safe while your thyroid is still sluggish? Or should you wait until your thyroid hormones are in better balance?

In this article, we’ll dive into why your thyroid gland plays a crucial role, how GLP-1 medications might interact with thyroid function, and what to know if you’re managing both your weight and a thyroid condition.

GLP-1 receptor agonists (GLP-1s) are a class of medications originally developed to treat type 2 diabetes, but they’ve also emerged as a transformative option for managing obesity and metabolic syndrome. These drugs mimic the action of glucagon-like peptide-1 (GLP-1), a naturally occurring hormone in the body that plays a key role in regulating blood sugar levels, satiety, and digestion.

When food is consumed, GLP-1 is secreted by the gut and helps coordinate several metabolic processes that maintain glucose balance and reduce food intake. GLP-1 receptor agonists enhance and extend these effects. Their main actions include:

• Slowing gastric emptying – This means food leaves the stomach more slowly, promoting a longer feeling of fullness after meals and reducing the post-meal rise in blood glucose.
• Suppressing appetite – By acting on the brain’s hunger centers, GLP-1s significantly reduce the desire to eat and help people consume fewer calories throughout the day.
• Enhancing insulin secretion in response to food – GLP-1s stimulate the pancreas to release insulin only when blood sugar levels are elevated, reducing the risk of hypoglycemia (low blood sugar).
• Suppressing glucagon – They decrease levels of glucagon, a hormone that normally signals the liver to release stored glucose, lowering fasting blood sugar levels.

These combined effects result in several clinically meaningful outcomes:

• Improved blood sugar control – For people with type 2 diabetes, GLP-1s help reduce both fasting and post-meal blood glucose, often allowing for a reduction in other medications.
• Substantial weight loss – Many people experience a reduction of 10 to 20% of their body weight over time, which can dramatically improve health outcomes related to obesity.
• Cardiovascular benefits – Certain GLP-1 agonists (such as semaglutide and liraglutide) have been shown to reduce the risk of major cardiovascular events, particularly in people with existing heart disease or high cardiovascular risk.

Given these benefits, GLP-1s are a powerful tool in the fight against obesity and metabolic dysfunction and have revolutionized treatments. They offer a holistic approach that addresses not just blood sugar control, but also weight, appetite regulation, and cardiovascular risk—critical factors in managing metabolic health.

However, when thyroid disease enters the picture, particularly autoimmune conditions like Hashimoto’s thyroiditis or concerns about thyroid nodules and cancer risk, the conversation around GLP-1s becomes more complex. Understanding how these medications interact with thyroid physiology—and what risks, if any, they may pose—is essential for making informed decisions about their use in individuals with thyroid disorders.

Thyroid disorders, including Hashimoto’s thyroiditis and hypothyroidism, are common in people with metabolic diseases like diabetes and obesity. Thyroid hormones—primarily T3 (triiodothyronine) and T4 (thyroxine)—play a vital role in regulating metabolism, energy expenditure, and insulin sensitivity.

When thyroid hormone levels are low (as in hypothyroidism or Hashimoto’s thyroiditis), metabolism slows down. Common consequences include:

• Weight gain or difficulty losing weight
• Fatigue and low energy
• Insulin resistance
• Constipation, dry skin, and cold intolerance
• Depression or brain fog

Notably, thyroid dysfunction can mask or worsen metabolic conditions like obesity, insulin resistance, and prediabetes—the very issues GLP-1 drugs aim to address. That’s why it’s crucial to understand how untreated or under-treated thyroid disease can affect the response to GLP-1 therapy.

Before initiating GLP-1 receptor agonist (GLP-1 RA) therapy, it is essential to consider whether thyroid function, particularly hypothyroidism, should be optimized first. The answer is yes. Addressing and optimizing thyroid function before starting GLP-1 RA therapy is critical in achieving the best possible outcomes. There are several reasons behind this recommendation.

Improved weight loss outcomes

Thyroid hormones are fundamental to metabolism and fat burning. If thyroid hormone levels are too low—either due to untreated hypothyroidism or suboptimal treatment—your basal metabolic rate drops. This means:

• You burn fewer calories at rest
• You’re more prone to retaining water and fat
• Weight loss is slower, even with reduced caloric intake

Studies suggest that untreated hypothyroidism can blunt the metabolic benefits of weight-loss interventions, including medication. Therefore, optimizing thyroid hormone levels may help maximize weight loss on a GLP-1. 

Reduced risk of side effects

GLP-1 medications can cause gastrointestinal side effects such as nausea, vomiting, diarrhea, constipation, and bloating. In hypothyroidism, slowed gut motility can intensify these issues. Constipation is already common in people with an underactive thyroid, and adding a medication that delays gastric emptying can worsen symptoms.

In addition, fatigue and brain fog – side effects sometimes reported with GLP-1s – may be worsened in people with untreated thyroid dysfunction, making it harder to tolerate treatment.

Better glycemic control

Thyroid function significantly affects insulin sensitivity. Hypothyroidism, even in its subclinical form, is associated with:

• Higher fasting insulin
• Increased HOMA-IR (a measure of insulin resistance)
• Elevated fasting glucose and hemoglobin A1C in some cases

While GLP-1s can improve glycemic control, their effectiveness may be reduced in the presence of uncontrolled thyroid disease. Optimizing thyroid hormone levels may enhance insulin sensitivity and improve the overall metabolic response to GLP-1 medications.

More accurate baseline lab values

If you start a GLP-1 while your thyroid is not yet stabilized or optimized, it can muddy the waters when interpreting lab values such as:

• Fasting insulin and glucose
• Lipid profiles
• Liver enzymes
• Inflammatory markers

Waiting until your thyroid hormones are optimized provides a more accurate baseline and makes it easier to measure how much the GLP-1 is helping, independently of thyroid effects.

Optimal thyroid function. It’s not just about having a TSH in the lab reference range. Many people feel unwell with a TSH of 4.0 to 5.0, even though it’s technically “normal.” Optimal thyroid function involves:

• TSH is between 0.5–2.5 mIU/L (some doctors and patients prefer a level below 2.0)
• Free T4 is in the upper half of the reference range
• Free T3 is in the upper half of the reference range
• Low or absent symptoms of hypothyroidism, such as fatigue, hair thinning, constipation, cold intolerance, or depression

In autoimmune thyroid disease (Hashimoto’s), it’s also helpful to monitor thyroid peroxidase (TPO) antibodies and support the immune system with selenium, vitamin D, and lifestyle changes to reduce inflammation.

Once these biomarkers are stable and symptoms are minimal, it’s usually safer and more effective to start a GLP-1.

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There are three ways that GLP-1s interact with thyroid function that require additional attention. 

Medullary thyroid cancer concerns

GLP-1 RAs carry a black box warning for thyroid C-cell tumors, including medullary thyroid carcinoma (MTC). This warning is based on rodent studies showing increased risk, although no clear link has been found in humans. Large cohort studies and meta-analyses show no substantial long-term increase in thyroid cancer risk with GLP-1 RA use. There is, however, a short-term spike in thyroid cancer diagnoses within the first year of initiation, likely due to increased surveillance (i.e., more thyroid ultrasounds and monitoring), not a direct causal effect.

Still, GLP-1s are contraindicated in people with a personal or family history of MTC or multiple endocrine neoplasia syndrome type 2 (MEN2).

This warning does not apply to Hashimoto’s thyroiditis or hypothyroidism caused by autoimmune or primary thyroid dysfunction.

Thyroid function changes

Some studies and case reports suggest GLP-1s may lower thyroid stimulating hormone (TSH) levels, possibly through direct effects on the hypothalamic-pituitary-thyroid (HPA) axis, and delayed gastric emptying (affecting medication absorption). While it’s not common, some patients on thyroid hormone replacement medication will require dose adjustments after starting GLP-1s.

This is why some clinicians, including Paloma health care providers who prescribe GLP-1 drugs, monitor thyroid function more closely after initiating a GLP-1. While no evidence shows that GLP-1s disrupt thyroid hormone levels, patients on thyroid medication should still monitor TSH, free thyroxine (Free T4), and free triiodothyronine (free T3) every 6 to 8 weeks when starting or adjusting therapy. Patients and practitioners should also watch for symptoms of over- or undertreatment of hypothyroidism. 

Weight loss affects dosage requirements

Weight loss can significantly affect thyroid medication dosage requirements. As fat mass decreases, inflammation levels often improve, and the body’s metabolic demands shift. This can result in a reduced need for thyroid hormone replacement, particularly in patients who initially required higher doses due to obesity-related factors like increased inflammation or altered hormone metabolism. Therefore, individuals on both thyroid medication and GLP-1s need their thyroid hormone levels monitored more frequently, as their dosage may need to be adjusted downward over time to avoid overtreatment. 

There are certain exceptions where a patient might start GLP-1 therapy before full thyroid optimization. 

Severe obesity or type 2 diabetes requiring urgent intervention

If a patient’s body mass index (BMI) is in the severe or morbid obesity range, or if they have uncontrolled type 2 diabetes with high blood sugar levels and/or A1C, waiting for thyroid stabilization could delay needed care. GLP-1s may help rapidly improve glycemic control and reduce cardiometabolic risk in these high-need cases.

Inability to lose weight despite thyroid hormone therapy

Some patients remain overweight or obese even after achieving optimal thyroid hormone levels. If thyroid labs are optimized but symptoms such as weight gain, insulin resistance, or metabolic syndrome persist, a GLP-1 medication may be introduced to break through the plateau and support weight reduction.

Very mild or subclinical hypothyroidism with no significant symptoms

In cases of subclinical hypothyroidism, where the TSH is slightly elevated but free T4 remains normal, and the patient has minimal or no symptoms, GLP-1 therapy may be started if there is a strong clinical indication such as prediabetes, elevated waist circumference, or high cardiovascular risk.

Access limitations or urgent medical need for metabolic control

In some real-world cases, patients may face barriers to thyroid care (such as long wait times for endocrinology appointments) but have immediate access to a weight loss or diabetes program that includes GLP-1 medications. If delaying treatment poses a greater health risk, a clinician may initiate a GLP-1 while continuing to work on thyroid stabilization in parallel.

Go “low and slow” 

In all of these situations, a “low and slow” approach is recommended when starting a GLP-1 medication. Begin with the lowest possible dose, increase gradually, and monitor closely for side effects, particularly gastrointestinal issues or changes in energy levels that could overlap with thyroid-related symptoms. It’s also essential to monitor thyroid function regularly, especially in the first few months of GLP-1 treatment.

Interestingly, in some patients, improving insulin sensitivity and reducing body fat through GLP-1 therapy may have positive downstream effects on thyroid health, potentially reducing systemic inflammation and improving autoimmune markers over time. However, there are no guarantees, so don’t assume this will happen. 

Ultimately, initiating GLP-1 therapy before full thyroid optimization is a clinical judgment call that should weigh the urgency of metabolic control against the risk of confusing the symptoms or destabilizing thyroid function. A coordinated, individualized treatment plan is key.

If you have thyroid disease and are considering starting a GLP-1 receptor agonist for weight management, a careful, stepwise approach can help ensure the best outcomes and minimize risks. Here’s a detailed plan, supported by current clinical guidance and research.

Step 1: Comprehensive thyroid workup

Before starting a GLP-1 medication, partner with your healthcare provider for a thorough thyroid evaluation. This should include:

• TSH
• Free T4 and free T3
• Reverse T3 
• Thyroid peroxidase (TPO) antibodies (to assess for autoimmune Hashimoto’s thyroid disease)
• Iron, ferritin, vitamin B12, vitamin D, and selenium levels

Thyroid dysfunction frequently co-occurs with metabolic diseases such as type 2 diabetes and obesity, and optimizing thyroid status is crucial for overall metabolic health. A comprehensive workup can identify both overt and subtle thyroid issues, as well as nutritional deficiencies that may impact thyroid function and overall well-being.

Step 2: Optimize thyroid hormone therapy

If you are already on thyroid hormone replacement, such as levothyroxine, liothyronine, or natural desiccated thyroid (NDT), your medication should be carefully adjusted to achieve optimal lab values and symptom control. This process may take several months, as dose changes require time to stabilize in the body and for symptoms to improve.

Achieving a stable and euthyroid (normal thyroid function) state is important because untreated or undertreated hypothyroidism can blunt the metabolic benefits of GLP-1 medications, such as weight loss and improved blood sugar control. Additionally, symptoms of hypothyroidism (like fatigue and constipation) can overlap with the side effects of GLP-1 RAs, making it difficult to distinguish between the two if thyroid function is not first optimized.

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‍Step 3: Reassess symptoms and labs

Once your thyroid function is stable and you feel better, it’s time to reassess your metabolic health. Your provider may order tests such as:

• Fasting glucose
• Fasting insulin or HOMA-IR (to assess insulin resistance)
• Hemoglobin A1C (for long-term blood sugar control)
• Lipid panel (cholesterol and triglycerides)
• Liver enzymes

This step ensures that your baseline metabolic status is well understood and that any improvements after starting a GLP-1 can be accurately attributed to the new medication, rather than to changes in thyroid therapy.

Step 4: Initiate GLP-1 therapy

With your thyroid function stabilized, you can begin GLP-1 therapy under medical supervision. It’s generally recommended to start at a low dose and titrate up gradually. This approach helps minimize common gastrointestinal side effects such as nausea, vomiting, and diarrhea, which are more likely when starting at higher doses.

GLP-1 medications are considered safe for most patients with Hashimoto’s or hypothyroidism, as long as there is no history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2, which are contraindications due to a potential cancer risk observed in animal studies.

Step 5: Monitor and adjust

Ongoing monitoring is essential after starting a GLP-1 medication:

• Check thyroid function every 6 to 8 weeks for the first few months, especially if you are on thyroid hormone replacement. GLP-1s can delay gastric emptying, which may affect the absorption of oral thyroid medications and necessitate dose adjustments.
• Monitor blood sugar, weight loss progress, and any side effects, particularly gastrointestinal symptoms.
• Stay alert for new or worsening symptoms of thyroid dysfunction, such as changes in energy, mood, or bowel habits.
• Your provider may recommend periodic reassessment of metabolic markers and nutritional status as your weight and metabolic health improve.

An important note: Remember that you lose a substantial amount of weight, you may need a reduction in your dose of thyroid hormone replacement medication. 

By following the steps in this plan, you can maximize the benefits of GLP-1 therapy while ensuring your thyroid health is well managed. Always consult your healthcare provider to tailor this approach to your unique needs and medical history.

At Paloma Health, we understand how truly interconnected your thyroid function and metabolic health are. Hypothyroidism doesn’t just make you feel tired or sluggish—it can significantly blunt weight loss efforts, disrupt blood sugar regulation, and intensify digestive issues. When unmanaged, these symptoms can undermine the full potential benefits of GLP-1 receptor agonists like semaglutide or tirzepatide.

That’s why we take a comprehensive, thyroid-first approach to metabolic care. Before starting GLP-1 therapy, we recommend optimizing your thyroid function. This proactive step helps ensure your body is primed to respond effectively to weight loss and blood sugar medications. It also reduces the risk of overlapping or confusing side effects, like nausea, constipation, fatigue, or hair thinning, symptoms common to both thyroid imbalance and GLP-1 medications.

At Paloma Health, you get more than just prescriptions. You get a partner. Our expert care team – including thyroid-savvy providers – works with you to regularly test, monitor, and fine-tune your thyroid levels. Once your thyroid function is stable, we can evaluate whether GLP-1 therapy is an appropriate and powerful next step in your journey toward metabolic health, sustainable weight loss, and improved quality of life.

Here’s what you can expect from working with Paloma Health:

• Comprehensive thyroid care, including convenient home thyroid testing, symptom tracking, and personalized treatment plans
• Metabolic health assessments to determine GLP-1 suitability and guide next steps
• Integrated, whole-body care that aligns your thyroid treatment with your weight loss and blood sugar goals
• Ongoing support and education, so you never feel like you’re navigating your health alone

Individualized care, consistent monitoring, and a deep understanding of how thyroid and metabolic systems interact are the foundation of our approach. With Paloma, you’re not just treating symptoms—you’re building a healthier future.

• Optimize thyroid health first. Treating hypothyroidism before starting a GLP-1 improves weight loss outcomes, insulin sensitivity, and minimizes side effects.
• GLP-1s can affect thyroid function. These medications may influence TSH levels and require dose adjustments for thyroid hormone replacement.
• GLP-1s are contraindicated in some thyroid cancers. They should be avoided in individuals with a personal or family history of medullary thyroid carcinoma or MEN2 syndrome.
• Starting GLP-1s may be appropriate in urgent cases. Severe obesity, uncontrolled diabetes, or subclinical hypothyroidism with minimal symptoms may justify early use of GLP-1s.
• Regular monitoring is essential. Thyroid labs (TSH, Free T4, Free T3) should be checked every 6–8 weeks when starting or adjusting GLP-1 or thyroid medications.
• A stepwise, individualized plan works best. Begin with a comprehensive thyroid workup, optimize hormone therapy, and introduce GLP-1s gradually if appropriate.