Weight loss injections, particularly GLP-1 receptor agonists such as semaglutide (Wegovy) and liraglutide (Saxenda), have transformed obesity management in the UK. As their use increases, patients often ask: do weight loss injections cause hair loss? Whilst hair thinning can occur during treatment, evidence suggests this is typically linked to rapid weight reduction itself rather than a direct medication effect. Understanding the relationship between these injections, weight loss, and hair health—alongside nutritional factors and management strategies—helps patients make informed decisions and seek appropriate support when needed.

Understanding Weight Loss Injections and Their Mechanism

Weight loss injections have become increasingly prominent in the management of obesity and type 2 diabetes in the UK. The most commonly prescribed medications in this category are GLP-1 receptor agonists (glucagon-like peptide-1 receptor agonists), which include semaglutide (marketed as Wegovy for weight loss) and liraglutide (Saxenda). Ozempic (semaglutide) is licensed only for type 2 diabetes treatment, not for weight loss. These medications are licensed by the Medicines and Healthcare products Regulatory Agency (MHRA) and recommended by NICE for specific patient groups.

These injections work by mimicking a naturally occurring hormone called GLP-1, which is released by the intestines after eating. The mechanism of action involves several physiological effects that contribute to weight loss:

• Appetite suppression: GLP-1 receptor agonists act on areas of the brain that regulate hunger, leading to reduced food intake and earlier satiety

• Delayed gastric emptying: The medication slows the movement of food from the stomach into the small intestine, prolonging feelings of fullness

• Improved insulin secretion: These drugs enhance glucose-dependent insulin release, which helps regulate blood sugar levels

• Reduced glucagon secretion: By suppressing this hormone, the liver produces less glucose

The weight loss effectiveness varies between medications. Clinical trials have shown semaglutide 2.4mg (Wegovy) achieves approximately 12-15% weight loss at around 68 weeks, while liraglutide 3.0mg (Saxenda) typically produces 5-8% weight loss at 56 weeks when combined with lifestyle modifications.

NICE guidelines recommend these medications as part of a comprehensive weight management programme delivered by specialist weight management services. For Wegovy, patients typically need a BMI ≥35 kg/m² with at least one weight-related comorbidity (with lower thresholds for certain groups), and treatment is usually limited to 2 years. For Saxenda, NICE recommends use in adults with prediabetes, high cardiovascular disease risk, and a BMI ≥35 kg/m², as part of a multicomponent weight management programme.

The Link Between Rapid Weight Loss and Hair Loss

Hair loss associated with significant weight reduction is a well-documented phenomenon known as telogen effluvium. This condition can occur regardless of the method used to lose weight—whether through bariatric surgery, very low-calorie diets, or pharmacological interventions. Understanding this connection is essential for patients using weight loss injections.

Telogen effluvium occurs when a significant proportion of hair follicles prematurely enter the telogen (resting) phase of the hair growth cycle. Normally, approximately 85-90% of scalp hair is in the anagen (growth) phase, with only 10-15% in telogen. However, physiological stress—including rapid weight loss—can trigger a substantial increase in follicles shifting into the resting phase simultaneously. This results in noticeable hair shedding approximately 2-4 months after the triggering event, which often coincides with the period of most rapid weight loss.

Several mechanisms explain why substantial weight reduction affects hair growth:

• Nutritional deficiencies: Rapid weight loss often leads to inadequate intake of protein, iron, zinc, and essential fatty acids—all crucial for healthy hair growth. While biotin is sometimes mentioned, deficiency is uncommon in the UK

• Caloric restriction: Severe energy deficit causes the body to prioritise vital functions over non-essential processes like hair growth

• Hormonal changes: Weight loss alters levels of thyroid hormones, oestrogen, and other endocrine factors that influence hair follicles

• Physical stress response: The body perceives rapid weight change as a stressor, triggering a systemic response that affects hair cycling

It is important to note that telogen effluvium is typically temporary and reversible. Hair growth usually resumes once weight stabilises and nutritional status improves, though recovery may take 6-12 months.

Clinical Evidence: Do GLP-1 Receptor Agonists Cause Hair Loss?

The question of whether weight loss injections directly cause hair loss requires careful examination of clinical evidence. Hair loss is not listed as a common adverse reaction in the UK Summary of Product Characteristics (SmPC) for semaglutide or liraglutide approved by the MHRA. However, patients should always check the most current SmPC information as these documents are periodically updated.

Clinical trial data from pivotal studies, including the STEP (Semaglutide Treatment Effect in People with obesity) programme and SCALE (Satiety and Clinical Adiposity—Liraglutide Evidence) trials, did not identify hair loss as a significant adverse event. These large-scale, randomised controlled trials involving thousands of participants monitored safety outcomes comprehensively. The most commonly reported side effects were gastrointestinal in nature—nausea, vomiting, diarrhoea, and constipation—rather than dermatological or hair-related issues.

However, post-marketing surveillance and patient reports have noted hair thinning among some individuals using these medications. This observation likely reflects the indirect association between the substantial weight loss achieved with these treatments and telogen effluvium, rather than a direct drug effect on hair follicles. The pharmacological mechanism of GLP-1 receptor agonists does not involve pathways known to affect hair growth directly.

A critical distinction must be made: the hair loss experienced by patients using weight loss injections appears to be a consequence of rapid weight reduction itself rather than a specific adverse effect of the medication. This is supported by the fact that similar rates of hair loss occur with other methods of achieving comparable weight loss. The temporal relationship—with hair shedding occurring several months into treatment when weight loss is most pronounced—further supports this interpretation.

Patients who experience hair loss or any other suspected side effects while taking these medications should report them through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk), which helps monitor medication safety.

Other Factors Contributing to Hair Loss During Weight Loss Treatment

When patients experience hair loss whilst using weight loss injections, multiple contributing factors beyond the weight reduction itself may be involved. A comprehensive assessment should consider these additional elements:

Nutritional deficiencies are particularly relevant. GLP-1 receptor agonists significantly reduce appetite and food intake, which can lead to inadequate consumption of essential nutrients. Key deficiencies associated with hair loss include:

• Protein: Hair is primarily composed of keratin, a protein structure requiring adequate dietary protein for synthesis

• Iron: Low ferritin levels can trigger telogen effluvium, even without frank anaemia

• Zinc: Essential for hair follicle function and protein synthesis

• Vitamin D: Plays a role in hair follicle cycling

• B vitamins: Important cofactors in cellular metabolism and hair growth

It's worth noting that while biotin is sometimes mentioned in relation to hair health, true biotin deficiency is rare in the UK. Additionally, high-dose biotin supplements can interfere with certain laboratory tests, including thyroid function and cardiac markers. Patients taking biotin supplements should inform healthcare professionals before blood tests, as advised by the MHRA.

Pre-existing medical conditions may be unmasked or exacerbated during weight loss treatment. Thyroid disorders, particularly hypothyroidism, commonly cause hair thinning and may coexist with obesity. Polycystic ovary syndrome (PCOS), iron deficiency anaemia, coeliac disease, and autoimmune conditions like alopecia areata should be considered in the differential diagnosis.

Medication interactions and concurrent treatments warrant evaluation. Patients may be taking other medications known to affect hair growth, including certain antihypertensives, antidepressants, or hormonal contraceptives. The cumulative effect of multiple factors may be more significant than any single cause.

Psychological stress associated with lifestyle changes, body image concerns, or the demands of a weight loss programme can independently trigger telogen effluvium. The physiological stress response activates hormonal pathways that affect hair follicle cycling.

Age and hormonal status also influence hair health. Perimenopausal and postmenopausal women may experience hair thinning related to declining oestrogen levels, which can coincide with weight management efforts. Understanding these multifactorial contributions helps guide appropriate investigation and management strategies.

Managing and Preventing Hair Loss While Using Weight Loss Injections

Proactive strategies can help minimise hair loss during weight loss treatment and support hair regrowth. A multifaceted approach addressing nutritional, lifestyle, and medical factors offers the best outcomes.

Nutritional optimisation is paramount. Patients should work with healthcare professionals, ideally a dietitian, to ensure adequate intake of essential nutrients:

• Protein: Aim for adequate protein intake based on individual needs (typically 0.8-1.2g per kilogram of body weight daily), distributed across meals. Include lean meats, fish, eggs, dairy, legumes, and plant-based protein sources

• Micronutrients: Focus on a balanced diet rich in iron, zinc, and vitamins. Supplementation should only be considered if dietary intake is insufficient or deficiencies are confirmed through testing

• Essential fatty acids: Omega-3 fatty acids from oily fish or supplements support scalp health

Blood tests to assess nutritional status may be appropriate, particularly measuring ferritin, vitamin B12, folate, and vitamin D levels. NICE guidance on obesity management emphasises the importance of nutritional adequacy during weight loss interventions.

Gradual, sustainable weight loss may reduce the physiological stress that triggers telogen effluvium. Whilst GLP-1 receptor agonists produce significant weight reduction, ensuring adequate nutrition to meet basic metabolic needs whilst still achieving weight loss can help. This should be individualised as part of a comprehensive weight management programme.

Hair care practices should be gentle during this period:

• Avoid excessive heat styling, tight hairstyles, and chemical treatments

• Use mild, sulphate-free shampoos

• Handle hair gently when wet, as it is more fragile

• Consider shorter hairstyles that may make thinning less noticeable

Stress management techniques, including adequate sleep, regular physical activity, and psychological support, can mitigate stress-related hair loss. Some patients benefit from mindfulness practices or cognitive behavioural approaches.

Currently, there is limited evidence supporting specific treatments for telogen effluvium related to weight loss, as the condition typically resolves spontaneously. Topical minoxidil might be considered after clinical assessment, but should not be used without healthcare professional advice. Dermatology referral may be appropriate for persistent cases.

When to Seek Medical Advice About Hair Loss

Whilst hair thinning during significant weight loss is often temporary and self-limiting, certain circumstances warrant medical evaluation. Patients should contact their GP if they experience:

Severe or progressive hair loss that continues beyond 6-8 months of stable weight, or worsens despite nutritional optimisation. Whilst telogen effluvium typically improves once the triggering factor resolves, persistent shedding may indicate an alternative diagnosis requiring investigation.

Patchy hair loss or bald spots rather than diffuse thinning. This pattern suggests conditions other than telogen effluvium, such as alopecia areata (an autoimmune condition), tinea capitis (fungal infection), or scarring alopecia. These conditions require specific dermatological assessment and treatment.

Associated symptoms that might indicate underlying medical conditions:

• Fatigue, cold intolerance, or weight changes suggesting thyroid dysfunction

• Unusual bruising, pallor, or extreme fatigue indicating possible anaemia

• Digestive symptoms that might suggest coeliac disease, particularly with iron deficiency

• Skin changes, joint pain, or other systemic symptoms that could reflect autoimmune disease

• Scalp symptoms including itching, scaling, redness, or tenderness

Significant psychological distress related to hair loss. Body image concerns and emotional wellbeing are important aspects of holistic care. Psychological support services may be beneficial, and in some cases, the risk-benefit balance of continuing weight loss treatment may need reassessment.

Diagnostic evaluation typically includes a thorough clinical history, examination of the scalp and hair, and blood tests to assess:

• Full blood count (to exclude anaemia)

• Ferritin levels (interpreted against local reference ranges)

• Thyroid function tests

• Vitamin B12 and folate

• Vitamin D

• Consider coeliac screening if iron deficiency is present

• Other tests as clinically indicated

Referral to dermatology may be appropriate for diagnostic uncertainty, treatment-resistant cases, or when specialist interventions are needed. The prescribing clinician should also review the overall weight loss treatment plan, ensuring it remains appropriate and that nutritional support is optimised. Remember that hair regrowth is a gradual process, and patience is essential—visible improvement typically takes 3-6 months once the underlying cause is addressed.

Frequently Asked Questions