Can Wegovy Cause Low Iron? Evidence and Guidance

Wegovy (semaglutide 2.4 mg) is a GLP-1 receptor agonist licensed in the UK for weight management in adults with obesity or overweight with weight-related comorbidities. Whilst Wegovy is highly effective for weight loss, patients and clinicians may wonder whether it can cause low iron levels. Iron deficiency is not listed as a recognised adverse effect in UK regulatory documentation, but the medication's gastrointestinal side effects and appetite-suppressing properties may indirectly affect nutritional status. This article examines the relationship between Wegovy and iron levels, explores potential mechanisms, and provides guidance on monitoring and managing nutritional health during treatment.

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Understanding Wegovy and Its Common Side Effects

Wegovy (semaglutide 2.4 mg) is a glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for weight management in adults with obesity or overweight with weight-related comorbidities. Administered as a once-weekly subcutaneous injection, Wegovy works by mimicking the natural hormone GLP-1, which regulates appetite and food intake. The medication slows gastric emptying, enhances satiety signals to the brain, and reduces hunger, leading to decreased caloric intake and subsequent weight loss.

The most frequently reported side effects of Wegovy are gastrointestinal in nature, affecting a significant proportion of users, particularly during dose escalation. According to the UK Summary of Product Characteristics (SmPC), these include:

• Nausea (very common: may affect more than 1 in 10 people)

• Diarrhoea (very common)

• Vomiting (very common)

• Constipation (very common)

• Abdominal pain and dyspepsia (common)

These gastrointestinal effects typically diminish over time as the body adjusts to the medication. Other common adverse reactions include headache, fatigue, and dizziness. More serious adverse effects include pancreatitis (reported but frequency not established), cholelithiasis (common), cholecystitis (uncommon), and hypoglycaemia (particularly in patients with type 2 diabetes taking concomitant insulin or sulfonylureas).

Patients experiencing severe gastrointestinal symptoms should maintain adequate hydration and seek medical advice if persistent, as dehydration may impact renal function.

The MHRA and EMA product information for Wegovy does not list iron deficiency or anaemia as a recognised adverse effect. However, the gastrointestinal side effects and dietary changes associated with significant weight loss may theoretically impact nutritional status, including micronutrient absorption and intake. Understanding the relationship between Wegovy and iron levels requires careful consideration of both direct pharmacological effects and indirect consequences of treatment.

Can Wegovy Cause Low Iron Levels?

There is no official link established between Wegovy and low iron levels based on current clinical trial data and regulatory documentation. Iron deficiency anaemia is not listed as a recognised adverse effect in the Summary of Product Characteristics (SmPC) approved by the MHRA or in the European Public Assessment Report (EPAR) from the EMA. The pivotal STEP (Semaglutide Treatment Effect in People with obesity) clinical trials, which enrolled over 4,500 participants, did not identify iron deficiency as a significant safety concern.

However, several indirect mechanisms may theoretically affect iron status in patients taking Wegovy:

Reduced dietary intake: The appetite-suppressing effects of semaglutide lead to substantially decreased food consumption. If patients do not maintain a nutritionally balanced diet despite eating less, they may inadvertently reduce their intake of iron-rich foods such as red meat, poultry, fish, legumes, and fortified cereals.

Gastrointestinal side effects: Persistent nausea, vomiting, and diarrhoea may limit food choices and reduce the absorption of nutrients, including iron. Chronic diarrhoea can impair iron absorption in the small intestine, whilst vomiting may prevent adequate dietary iron intake.

It is important to distinguish between a direct drug effect and the nutritional consequences of rapid weight loss and dietary restriction. If iron deficiency is detected in a patient taking Wegovy, clinicians should evaluate for other common causes (such as gastrointestinal blood loss) rather than attributing the deficiency to the medication by default. Any concerns about iron levels should be discussed with a healthcare professional who can assess individual risk factors and nutritional status.

Nutritional Deficiencies and GLP-1 Receptor Agonists

Weight loss interventions, whether pharmacological or surgical, carry inherent risks of nutritional deficiencies if not properly managed. Whilst GLP-1 receptor agonists like Wegovy do not directly interfere with nutrient absorption in the same manner as bariatric surgery, the substantial caloric restriction they facilitate can lead to inadequate micronutrient intake.

Iron requirements and sources: According to NHS guidance, adults require approximately 8.7 mg of iron daily (men and post-menopausal women) or 14.8 mg daily (menstruating women). Iron exists in two dietary forms:

• Haem iron (from meat, poultry, fish) – more readily absorbed

• Non-haem iron (from plant sources, fortified foods) – less efficiently absorbed

Patients on Wegovy who significantly reduce their overall food intake or adopt restrictive eating patterns may struggle to meet these requirements. Menstruating women, vegetarians, and vegans are at particularly elevated risk of iron deficiency due to higher requirements or reliance on less bioavailable iron sources.

To improve iron absorption, patients should combine plant-based iron sources with vitamin C-rich foods, avoid drinking tea or coffee with meals, and separate calcium intake from iron-rich meals.

Beyond iron, other nutrients of concern during significant weight loss include:

• Vitamin B12 (particularly in those reducing meat intake)

• Vitamin D and calcium (important for bone health)

• Folate, thiamine, and other B vitamins

• Protein (essential for preserving lean muscle mass)

NICE guidance on obesity management (CG189) emphasises the importance of nutritional adequacy during weight loss interventions. Healthcare professionals should encourage patients taking Wegovy to maintain a varied, nutrient-dense diet and consider referral to a registered dietitian for personalised nutritional counselling, particularly for those with pre-existing deficiencies or at higher risk of malnutrition.

Monitoring Iron Levels While Taking Wegovy

Routine iron monitoring is not mandated for all patients taking Wegovy, but individualised assessment based on risk factors and symptoms may be appropriate, particularly for those at higher risk of deficiency.

Who may benefit from iron status assessment?

• Menstruating women (especially those with heavy menstrual bleeding)

• Individuals with pre-existing anaemia or known iron deficiency

• Vegetarians and vegans with limited dietary iron sources

• Patients with malabsorption disorders (coeliac disease, inflammatory bowel disease)

• Those experiencing persistent gastrointestinal side effects

• Individuals with a history of bariatric surgery

Appropriate investigations for suspected iron deficiency include:

• Full blood count (FBC): Identifies anaemia (low haemoglobin) and may show microcytic, hypochromic red cells

• Serum ferritin: The most specific test for iron stores

• Transferrin saturation: Provides additional information about iron availability (values <20% support iron deficiency)

• Total iron-binding capacity (TIBC): Typically elevated in iron deficiency

According to NICE Clinical Knowledge Summary on iron deficiency anaemia, ferritin thresholds vary by clinical context: <15 micrograms/L is highly specific for iron deficiency; <30 micrograms/L increases sensitivity in most adults; higher thresholds (e.g., <50 micrograms/L) may be appropriate if inflammation is suspected.

Investigation of confirmed iron deficiency: The British Society of Gastroenterology (BSG) recommends that all adults with iron deficiency anaemia should be screened for coeliac disease. Additionally, adult men and post-menopausal women with iron deficiency anaemia should undergo appropriate gastrointestinal evaluation to exclude underlying causes such as gastrointestinal blood loss. NICE guideline NG12 recommends urgent suspected cancer referral for adults aged 60 and over with iron deficiency anaemia.

Patients with confirmed deficiency require appropriate iron supplementation and investigation of underlying causes beyond medication effects. Healthcare professionals should consider the individual's clinical picture when determining the appropriate monitoring approach.

When to Seek Medical Advice About Iron Deficiency

Patients taking Wegovy should be aware of the signs and symptoms of iron deficiency anaemia and know when to contact their GP or prescribing clinician. Early recognition and treatment can prevent progression to more severe anaemia and its associated complications.

Symptoms warranting medical review include:

• Persistent fatigue and weakness beyond what might be expected from dietary changes

• Breathlessness on minimal exertion or at rest

• Palpitations or awareness of rapid heartbeat

• Pale skin, nail beds, or conjunctivae

• Headaches and dizziness, particularly on standing

• Cold hands and feet

• Restless legs syndrome or unusual cravings (pica)

• Sore or smooth tongue (glossitis)

• Brittle nails or hair loss

Urgent medical attention is required if patients experience:

• Severe breathlessness or chest pain

• Syncope (fainting) or pre-syncope

• Signs of gastrointestinal bleeding (black or very dark stools, persistent change in bowel habit)

• Unintentional weight loss not attributable to Wegovy

• Visible rectal bleeding

Patients should not self-diagnose or self-treat with over-the-counter iron supplements without medical advice, as excessive iron intake can cause gastrointestinal side effects and mask underlying conditions requiring investigation. Furthermore, iron deficiency may result from causes unrelated to Wegovy, such as gastrointestinal bleeding, which requires prompt evaluation.

Healthcare professionals should:

• Provide clear safety-netting advice about nutritional concerns

• Encourage maintenance of a balanced, nutrient-rich diet

• Consider dietitian referral for vulnerable patients

• Investigate and treat confirmed iron deficiency appropriately

• Follow NICE and BSG guidance for investigation of iron deficiency anaemia

• Review the risk-benefit profile of continuing Wegovy if nutritional deficiencies prove difficult to manage

If patients suspect they are experiencing side effects from Wegovy, they or their healthcare professional can report these through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Maintaining open communication between patients and healthcare providers ensures that any nutritional concerns are addressed promptly whilst maximising the benefits of weight management therapy.

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