Levothyroxine and Saxenda together may be prescribed when patients with well-controlled hypothyroidism require weight management treatment. Levothyroxine is a synthetic thyroid hormone used to treat underactive thyroid, whilst Saxenda (liraglutide 3mg) is a GLP-1 receptor agonist licensed for weight management in adults with obesity or overweight with comorbidities. There is no formal contraindication to concurrent use, though appropriate medical supervision and monitoring are essential. This article examines the safety considerations, monitoring requirements, and practical guidance for patients taking both medications simultaneously under NHS care.

Understanding Levothyroxine and Saxenda: Different Medications with Distinct Purposes

Levothyroxine and Saxenda are two fundamentally different medications prescribed for distinct medical conditions, though patients may occasionally require both simultaneously.

Levothyroxine is a synthetic thyroid hormone (thyroxine, T4) used as hormone replacement therapy for hypothyroidism—a condition where the thyroid gland produces insufficient thyroid hormone. This medication works by supplementing or replacing the body's natural thyroid hormone, thereby restoring normal metabolic function. Levothyroxine is essential for regulating metabolism, energy production, and numerous bodily functions. Patients with hypothyroidism typically require lifelong treatment, with dosing carefully titrated based on thyroid function tests (TSH, free T4). The medication is licensed by the MHRA and widely prescribed across the NHS for various forms of thyroid insufficiency, including autoimmune thyroiditis (Hashimoto's disease), post-thyroidectomy states, and radioiodine treatment.

Saxenda (liraglutide 3mg) is a glucagon-like peptide-1 (GLP-1) receptor agonist licensed for weight management in adults with obesity (BMI ≥30 kg/m²) or overweight individuals (BMI ≥27 kg/m²) with weight-related comorbidities such as type 2 diabetes, hypertension, or dyslipidaemia. Saxenda is administered as a once-daily subcutaneous injection, with dose gradually titrated weekly up to the 3mg maintenance dose. It works by mimicking the natural hormone GLP-1, which regulates appetite and food intake. It slows gastric emptying, increases satiety, and reduces hunger signals to the brain.

According to NICE Technology Appraisal (TA664), Saxenda is available through NHS specialist weight management services, typically for up to 2 years, with specific eligibility criteria. Treatment should be alongside dietary modification and increased physical activity.

Saxenda is not recommended during pregnancy or breastfeeding. Women of childbearing potential should use effective contraception while taking Saxenda. Levothyroxine is generally safe during pregnancy, though dose requirements often increase and require monitoring.

Understanding these distinct mechanisms is crucial—levothyroxine addresses hormonal deficiency, whilst Saxenda targets weight management through appetite regulation. Neither medication treats the other's primary indication.

Can You Take Levothyroxine and Saxenda Together?

There is no formal contraindication to taking levothyroxine and Saxenda concurrently, though no extensive clinical studies have specifically examined this combination. Patients with well-controlled hypothyroidism who meet the criteria for weight management treatment may be prescribed both medications simultaneously under appropriate medical supervision.

While the medications have different mechanisms of action, some caution is warranted. Saxenda slows gastric emptying, which could theoretically affect the absorption timing of oral medications like levothyroxine. This doesn't constitute a direct interaction, but it's a consideration for monitoring.

Key considerations for concurrent use:

• Both medications can be prescribed together when clinically indicated

• Thyroid function should be monitored when starting or changing Saxenda doses

• TSH (and possibly free T4) should be checked 6-8 weeks after starting or titrating Saxenda

• Significant weight loss may alter levothyroxine requirements in some patients

• Thyroid function should be reassessed after substantial weight changes

It is essential that prescribing decisions are made by qualified healthcare professionals who can assess individual patient circumstances, including thyroid status, cardiovascular health, and weight management goals. Patients should never initiate, stop, or modify either medication without medical guidance. The decision to use both medications should follow NICE guidance for weight management (TA664) and thyroid disorder management (NG145), with clear therapeutic goals established at the outset.

Important Considerations When Using Both Medications

When taking levothyroxine and Saxenda together, several important clinical and practical considerations require attention to ensure safe and effective treatment.

Timing of Levothyroxine Administration

Levothyroxine should be taken consistently, ideally on an empty stomach, 30–60 minutes before breakfast or at bedtime (at least 3–4 hours after the last meal). This timing optimises absorption and maintains stable thyroid hormone levels. Patients should maintain their established levothyroxine routine when starting Saxenda, as consistency is crucial for thyroid management.

Levothyroxine should be separated by at least 4 hours from iron supplements, calcium supplements, antacids containing aluminium or magnesium, and bile acid sequestrants, as these can significantly reduce absorption.

Gastrointestinal Effects

Saxenda commonly causes gastrointestinal adverse effects, particularly during dose titration. These include:

• Nausea (very common, affecting more than 1 in 10 patients)

• Vomiting and diarrhoea

• Constipation

• Abdominal discomfort

These effects may temporarily affect appetite and eating patterns. Whilst this does not directly impact levothyroxine efficacy, severe or persistent vomiting could theoretically affect absorption if levothyroxine is taken during symptomatic periods. Patients experiencing significant gastrointestinal symptoms should consult their GP and maintain adequate hydration to prevent dehydration and potential renal issues.

Cardiovascular Considerations

Both medications require cardiovascular awareness. Excessive levothyroxine can cause palpitations, tachycardia, and arrhythmias, whilst Saxenda may increase heart rate (average increase of 2–3 beats per minute). Patients with pre-existing cardiovascular disease require careful assessment before starting Saxenda. Any symptoms of chest pain, palpitations, or unusual breathlessness warrant immediate medical review.

Weight Loss and Thyroid Function

Successful weight loss with Saxenda does not typically alter levothyroxine requirements in patients with primary hypothyroidism, as the underlying thyroid pathology remains unchanged. However, thyroid function tests should be monitored according to standard protocols and after significant weight changes. Some patients may have been diagnosed with subclinical hypothyroidism in the context of obesity, and significant weight loss could potentially affect thyroid parameters—though this remains an area requiring individualised assessment.

Monitoring and Medical Supervision Requirements

Concurrent use of levothyroxine and Saxenda necessitates appropriate monitoring to ensure both therapeutic efficacy and patient safety. Each medication requires specific surveillance parameters.

Thyroid Function Monitoring

For patients established on levothyroxine, thyroid function tests (TSH and free T4) should be monitored according to standard protocols:

• Every 6–12 months once stable on an established dose

• 6–8 weeks after any dose adjustment

• 6–8 weeks after starting or changing the dose of Saxenda

• After significant weight loss or gain

• More frequently if symptoms of hypo- or hyperthyroidism develop

Patients should report symptoms suggesting inadequate thyroid replacement (fatigue, cold intolerance, weight gain, constipation) or excessive replacement (palpitations, tremor, anxiety, heat intolerance, unintentional weight loss).

Saxenda Treatment Monitoring

According to the Summary of Product Characteristics and NICE TA664, Saxenda treatment requires:

• Assessment of weight loss response after 12 weeks at the 3mg maintenance dose

• Discontinuation if patients have not lost at least 5% of initial body weight

• Regular review of cardiovascular risk factors

• Monitoring for adverse effects, particularly gastrointestinal symptoms

• Assessment of heart rate, especially in patients with cardiac history

• Treatment typically limited to a maximum of 2 years in NHS specialist services

Women of childbearing potential should use effective contraception while taking Saxenda and have pregnancy testing as appropriate. Saxenda should be avoided during pregnancy and breastfeeding.

Integrated Clinical Review

Patients taking both medications benefit from coordinated care:

• Regular GP or specialist review (frequency determined by individual circumstances)

• Blood pressure monitoring

• Assessment of weight management progress and metabolic parameters

• Review of medication adherence and technique (particularly Saxenda injection technique)

• Evaluation of overall treatment goals and quality of life

Patients should maintain open communication with their healthcare team, reporting any concerns, side effects, or changes in symptoms promptly. Medication reviews provide opportunities to assess whether both treatments remain clinically appropriate and to adjust management plans accordingly.

When to Seek Medical Advice

Patients taking levothyroxine and Saxenda together should be aware of specific situations requiring medical attention. Understanding when to contact healthcare services ensures timely intervention and optimal safety.

Urgent Medical Attention Required

Seek immediate medical help (call 999 or attend A&E) if experiencing:

• Severe chest pain or pressure

• Severe allergic reaction (anaphylaxis): difficulty breathing, swelling of face/throat, severe rash

• Symptoms of thyroid storm (rare but serious): high fever, severe agitation, rapid heartbeat, confusion

• Severe, persistent abdominal pain (potential pancreatitis—a rare but serious Saxenda adverse effect)

• Persistent vomiting preventing fluid or medication intake

• Suicidal thoughts or behaviour (discontinue Saxenda immediately and seek urgent help)

Contact Your GP Promptly

Arrange a GP appointment within a few days if experiencing:

• New or worsening symptoms suggesting thyroid dysfunction (unusual fatigue, significant mood changes, palpitations, tremor)

• Persistent gastrointestinal symptoms affecting quality of life or nutrition

• Signs of dehydration from vomiting or diarrhoea

• Unexplained weight changes inconsistent with treatment expectations

• New or increased heart rate or palpitations

• Symptoms of gallbladder disease (upper abdominal pain, particularly after eating)

• Mood changes or depression

Routine Medication Reviews

Schedule regular appointments to discuss:

• Effectiveness of weight management treatment

• Thyroid symptom control and blood test results

• Any side effects or tolerability concerns

• Questions about medication administration or lifestyle modifications

• Whether continuation of Saxenda remains appropriate based on weight loss response

Patients should never stop levothyroxine abruptly, as this can lead to hypothyroid symptoms. Similarly, Saxenda discontinuation should be discussed with the prescribing clinician.

Suspected side effects can be reported via the MHRA Yellow Card scheme (www.mhra.gov.uk/yellowcard or the Yellow Card app).

Maintaining regular contact with healthcare providers, attending scheduled monitoring appointments, and reporting concerns promptly ensures safe, effective management when taking both medications together. Your healthcare team can provide personalised advice based on your individual medical history and treatment response.

Frequently Asked Questions