Can Weight Loss Injections Make You Tired? Causes and Management

Weight loss injections, particularly GLP-1 receptor agonists such as semaglutide (Wegovy) and liraglutide (Saxenda), can indeed cause tiredness in some patients. Fatigue is recognised as a common adverse reaction, affecting up to 8% of people according to clinical trial data and product information approved by the MHRA. This tiredness may result from reduced caloric intake, gastrointestinal side effects, metabolic adjustments, or dehydration. Whilst most patients find that initial fatigue improves within 4–8 weeks as the body adapts, persistent or severe tiredness warrants medical review to exclude other causes and ensure safe continuation of treatment.

Understanding Weight Loss Injections and Fatigue

Weight loss injections, particularly glucagon-like peptide-1 (GLP-1) receptor agonists such as semaglutide (Wegovy) and liraglutide (Saxenda), have become increasingly prescribed for weight management in the UK. These medications work by mimicking natural hormones that regulate appetite and blood glucose levels. Whilst these injections can be highly effective for weight reduction, some patients report experiencing tiredness or fatigue during treatment.

Fatigue and tiredness are listed as common adverse reactions in the Summary of Product Characteristics (SmPC) for both semaglutide (Wegovy) and liraglutide (Saxenda) as approved by the Medicines and Healthcare products Regulatory Agency (MHRA). Clinical experience suggests that tiredness may be particularly noticeable during the initial weeks of treatment. Understanding whether this fatigue is directly caused by the medication itself or results from associated factors is essential for appropriate management.

The relationship between weight loss injections and tiredness is multifactorial. Several mechanisms may contribute to feelings of fatigue, including:

• Reduced caloric intake due to appetite suppression

• Gastrointestinal side effects affecting food and fluid intake

• Changes in blood glucose regulation

• Adjustment period as the body adapts to metabolic changes

• Dehydration from nausea or reduced fluid intake

It is important to distinguish between normal tiredness during weight loss and fatigue that may indicate an underlying medical concern. Many patients find that initial tiredness improves as their body adjusts to the medication, typically within the first few weeks of starting treatment. However, persistent or severe fatigue warrants medical review to exclude other causes and ensure safe continuation of therapy.

Why Weight Loss Injections May Cause Tiredness

The mechanisms by which weight loss injections may contribute to tiredness are complex and often indirect. GLP-1 receptor agonists work through multiple pathways: they suppress appetite through central brain effects, delay gastric emptying, and enhance glucose-dependent insulin secretion while suppressing glucagon. These actions lead to significantly decreased food intake. This caloric restriction, whilst beneficial for weight loss, can result in reduced energy availability, particularly if nutritional intake becomes inadequate or unbalanced.

When caloric intake drops substantially, the body may experience a temporary energy deficit whilst it adapts to using stored fat for fuel. This metabolic transition can manifest as fatigue, especially in the first few weeks of treatment. Additionally, gastrointestinal side effects—including nausea, vomiting, and diarrhoea—are common with GLP-1 medications and can contribute to tiredness through dehydration and reduced food intake.

Another consideration is the impact on blood glucose regulation. Whilst GLP-1 receptor agonists help stabilise blood sugar levels, some patients may experience changes in glucose levels as their body adjusts. It's important to note that significant hypoglycaemia is uncommon with these medications unless they are combined with insulin or sulfonylureas, or during prolonged fasting. However, even modest changes in usual glucose patterns may temporarily affect energy levels in some individuals.

Nutritional inadequacy may develop if dietary intake becomes too restricted or lacks variety. Insufficient protein, iron, vitamin B12, or other essential nutrients can all cause fatigue. Furthermore, rapid weight loss itself—regardless of the method—is associated with temporary tiredness as the body undergoes significant metabolic and hormonal changes. These adjustments commonly include fatigue as a transient symptom.

Types of Weight Loss Injections and Their Fatigue Risk

Different weight loss injections have varying profiles regarding fatigue and tiredness. Semaglutide (Wegovy) is a once-weekly GLP-1 receptor agonist licensed for weight management in adults with a BMI ≥30 kg/m² or ≥27 kg/m² with weight-related comorbidities. According to the UK SmPC, fatigue is listed as a common side effect (affecting up to 1 in 10 people). Gastrointestinal symptoms are very common, with nausea affecting approximately 1 in 3 patients in clinical trials. The once-weekly dosing and gradual dose escalation protocol may help minimise side effects.

Liraglutide (Saxenda) is administered daily and works through similar mechanisms to semaglutide. The SmPC lists fatigue as a common side effect, while nausea, vomiting, and diarrhoea are very common side effects (affecting more than 1 in 10 people). These gastrointestinal symptoms can contribute to feelings of tiredness. Some patients report that the daily injection schedule may affect their energy levels differently than weekly preparations, though individual experiences vary considerably.

Tirzepatide, a dual GIP/GLP-1 receptor agonist, has been approved in the UK for type 2 diabetes (as Mounjaro) but at the time of writing is not licensed by the MHRA specifically for weight management. Clinical trials suggest a similar side effect profile to other GLP-1 medications, including fatigue and gastrointestinal symptoms, though direct comparisons should be interpreted cautiously until UK-specific weight management guidance is available.

Individual variation is considerable—some patients experience no tiredness whatsoever, whilst others find fatigue significantly impacts their quality of life. Factors influencing fatigue risk include:

• Starting dose and escalation speed

• Baseline nutritional status

• Concurrent medications

• Pre-existing medical conditions

• Adequacy of dietary intake during treatment

Patients should discuss their specific medication and individual risk factors with their prescribing clinician before commencing treatment.

Managing Fatigue While Using Weight Loss Injections

If you experience tiredness whilst using weight loss injections, several evidence-based strategies can help manage this symptom effectively. Maintaining adequate nutrition is paramount—despite reduced appetite, it is essential to consume sufficient calories and nutrients to support basic metabolic functions. Focus on nutrient-dense foods that provide maximum nutritional value in smaller portions, including lean proteins, whole grains, fruits, vegetables, and healthy fats.

Protein intake deserves particular attention. While specific gram targets vary by individual needs, consuming adequate protein helps preserve lean muscle mass during weight loss. The British Dietetic Association recommends including protein sources at each meal. Good options include fish, poultry, eggs, legumes, and dairy products. If you have kidney disease or other health conditions, discuss appropriate protein intake with your healthcare provider or dietitian.

Hydration is crucial, especially if experiencing gastrointestinal side effects. Dehydration can significantly worsen fatigue. Aim for 6–8 glasses of fluid daily, adjusting for activity level and climate. If plain water is difficult to tolerate due to nausea, try:

• Herbal teas

• Diluted fruit juice

• Clear broths

• Water with fresh lemon or cucumber

If experiencing persistent vomiting or diarrhoea, consider oral rehydration solutions and seek medical advice.

Gradual dose escalation, as recommended in prescribing guidelines, allows your body to adapt to the medication and may reduce the severity of side effects, including fatigue. Never increase your dose faster than prescribed, even if weight loss seems slow initially.

Regular physical activity, whilst challenging when tired, can paradoxically improve energy levels. Start with gentle activities such as walking for 10–15 minutes daily and gradually increase as tolerated. Exercise improves cardiovascular fitness, mood, and sleep quality—all factors that influence fatigue.

Sleep hygiene should not be overlooked. Aim for 7–9 hours of quality sleep nightly, maintain a consistent sleep schedule, and create a restful bedroom environment. Some patients find that timing their injection to minimise overnight nausea improves sleep quality.

If you have diabetes and take insulin or sulfonylureas, monitor your blood glucose levels carefully and discuss medication adjustments with your healthcare provider, as reduced food intake may increase hypoglycaemia risk.

Consider keeping a symptom diary to identify patterns—noting when fatigue is worst, what you've eaten, hydration status, and sleep quality can help you and your healthcare provider identify contributing factors and develop targeted management strategies.

If you experience side effects that you suspect are related to your medication, report them through the MHRA Yellow Card Scheme.

When to Seek Medical Advice About Tiredness

Whilst mild tiredness during the initial weeks of weight loss injection therapy may be expected, certain symptoms warrant prompt medical review. Contact your GP or prescribing clinician if you experience:

• Severe or worsening fatigue that significantly impairs daily activities or persists beyond several weeks of treatment

• Extreme weakness or inability to perform usual tasks

• Dizziness or fainting, particularly on standing, which may indicate dehydration or blood pressure changes

• Persistent nausea or vomiting preventing adequate food or fluid intake

• Signs of dehydration: dark urine, reduced urination, dry mouth, confusion

• Chest pain, palpitations, or breathlessness accompanying tiredness

• Mood changes, including low mood or depression, which can manifest as fatigue

• Right upper abdominal pain, fever or yellowing of the skin/eyes, which could indicate gallbladder problems (GLP-1 medications may increase gallstone risk)

For urgent but non-emergency concerns, you can contact NHS 111 for advice.

Seek urgent medical attention (call 999 or attend A&E) if you experience:

• Severe abdominal pain, particularly if accompanied by vomiting

• Signs of pancreatitis: severe upper abdominal pain radiating to the back

• Symptoms of severe dehydration: confusion, rapid heartbeat, very low urine output

• Allergic reactions: difficulty breathing, facial swelling, severe rash

Your healthcare provider may wish to investigate potential underlying causes of fatigue through blood tests, including:

• Full blood count (to check for anaemia)

• Thyroid function tests

• Vitamin B12 and folate levels

• Iron studies

• Kidney and liver function

• HbA1c (if diabetic or pre-diabetic)

In some cases, dose adjustment or temporary treatment interruption may be necessary to allow recovery from side effects. Never stop your medication without medical advice, as abrupt discontinuation may affect your weight management plan. Your prescriber can work with you to find the optimal balance between effective weight loss and manageable side effects, potentially adjusting the dose, changing the injection timing, or considering alternative treatments if fatigue remains problematic despite management strategies. Regular follow-up appointments, as recommended in NICE guidance for weight management services, ensure ongoing monitoring and support throughout your treatment journey.

Scientific References

1. Ozempic | European Medicines Agency (EMA).
2. Semaglutide | Drugs | BNF | NICE.
3. Obesity: identification, assessment and management.
4. Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management.
5. British Dietetic Association evidence-based guidelines for the protein requirements of adults undergoing maintenance haemodialysis or peritoneal dialysis.
6. Myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) - Diagnosis.
7. GLP-1 medicines for weight loss and diabetes: what you need to know.

Frequently Asked Questions