GLP-1 receptor agonists such as semaglutide (Ozempic, Wegovy), dulaglutide (Trulicity), and liraglutide (Victoza, Saxenda) are increasingly prescribed in the UK for type 2 diabetes and weight management. Whilst generally well-tolerated, some patients report experiencing tiredness during treatment. Fatigue is listed as a common adverse reaction in the Summary of Product Characteristics for several GLP-1 medications, particularly at higher doses used for weight management. This tiredness can occur directly as a side effect or indirectly through reduced caloric intake, gastrointestinal symptoms, or low blood glucose levels. Understanding why fatigue occurs and how to manage it effectively can help patients optimise their treatment experience whilst maintaining therapeutic benefits.
Quick Answer: GLP-1 injections can cause tiredness, classified as a common side effect affecting between 1 in 10 and 1 in 100 people, particularly at higher doses used for weight management.
Glucagon-like peptide-1 (GLP-1) receptor agonists are injectable medications increasingly prescribed for type 2 diabetes management and, more recently, weight management. Commonly used GLP-1 medications in the UK include semaglutide (Ozempic, Wegovy), dulaglutide (Trulicity), and liraglutide (Victoza, Saxenda). Whilst these treatments are generally well-tolerated and effective, some patients report experiencing tiredness or fatigue during treatment.
Fatigue is actually listed as a common adverse reaction in the Summary of Product Characteristics (SmPC) for some GLP-1 receptor agonists, particularly those used at higher doses for weight management such as semaglutide 2.4mg (Wegovy) and liraglutide 3mg (Saxenda). The most frequently reported side effects typically include gastrointestinal symptoms such as nausea, vomiting, diarrhoea, and constipation, which affect a significant proportion of patients, particularly during dose escalation. Fatigue can occur both as a direct side effect and indirectly through several mechanisms related to how these medications work.
GLP-1 receptor agonists function by mimicking the action of the naturally occurring GLP-1 hormone. They slow gastric emptying, enhance insulin secretion in response to meals, suppress glucagon release, and reduce appetite through effects on the central nervous system. These mechanisms contribute to improved glycaemic control and weight loss, but they can also lead to reduced caloric intake, changes in eating patterns, and occasionally low blood glucose levels (hypoglycaemia), all of which may contribute to feelings of tiredness.
It is important to note that the frequency of fatigue varies between different GLP-1 products and doses, with higher rates typically seen with the weight management doses compared to the lower doses used for diabetes treatment.
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Start HereFatigue is reported with varying frequency across different GLP-1 receptor agonists. In clinical trials such as the STEP programme for semaglutide 2.4mg (Wegovy), fatigue was reported more frequently in patients receiving the active treatment compared to placebo. According to the UK SmPC for Wegovy, fatigue is classified as a 'common' side effect (affecting between 1 in 10 and 1 in 100 people). Similarly, the SCALE trials for liraglutide 3mg (Saxenda) documented fatigue as a common adverse reaction.
Several factors may explain why some individuals experience fatigue whilst taking GLP-1 medications:
Reduced caloric intake: The appetite-suppressing effects can lead to significantly lower food consumption, potentially resulting in inadequate energy intake, particularly if patients are not consuming balanced, nutrient-dense meals.
Rapid weight loss: Patients losing weight quickly may experience temporary fatigue as the body adapts to metabolic changes and reduced energy stores.
Gastrointestinal symptoms: Persistent nausea, vomiting, or diarrhoea can lead to dehydration, electrolyte imbalances, and reduced nutrient absorption, all contributing to tiredness.
Hypoglycaemia: GLP-1 agonists have a low intrinsic risk of causing low blood glucose when used alone. However, patients taking them alongside other diabetes medications (particularly insulin or sulphonylureas) have an increased risk of hypoglycaemic episodes, which commonly present with fatigue, weakness, and confusion.
Patient-reported experiences vary considerably. Some individuals report feeling more energetic due to improved glycaemic control and weight loss, whilst others may notice increased tiredness, particularly in the early treatment phase. Individual responses to GLP-1 therapy are influenced by baseline health status, concurrent medications, dietary habits, and lifestyle factors. If fatigue persists beyond the initial adjustment period or significantly impacts daily functioning, further evaluation is warranted to identify underlying causes.
If you experience tiredness whilst taking GLP-1 injections, several practical strategies may help manage this symptom effectively:
Nutritional considerations are paramount. Despite reduced appetite, it is essential to maintain adequate caloric and nutritional intake. Focus on consuming nutrient-dense foods including lean proteins, whole grains, fruits, vegetables, and healthy fats in line with the NHS Eatwell Guide. Small, frequent meals may be better tolerated than larger portions, particularly if nausea is present. Ensure adequate protein intake (typically 0.8-1.2g per kilogram of ideal body weight daily, though requirements vary individually) to preserve muscle mass during weight loss and support energy levels. Those with kidney disease or other health conditions may need personalised advice from a dietitian.
Hydration is equally important. Aim for at least 1.5–2 litres of fluid daily, increasing this amount if experiencing diarrhoea or vomiting. If you have heart failure or kidney disease, discuss appropriate fluid intake with your healthcare team. Dehydration can significantly contribute to fatigue and may exacerbate other side effects. Water is preferable, though sugar-free squash or herbal teas are acceptable alternatives.
Monitor blood glucose levels regularly, particularly if you are taking other diabetes medications. If you experience symptoms suggestive of hypoglycaemia (tiredness, shakiness, sweating, confusion), check your blood glucose and treat appropriately with 15-20g of fast-acting carbohydrate (e.g., glucose tablets, fruit juice) if levels are below 4 mmol/L. Recheck after 10-15 minutes and follow with a starchy snack if your next meal is not due. Your diabetes care team may need to adjust doses of concurrent medications to reduce hypoglycaemia risk.
Gradual dose escalation is standard practice with GLP-1 medications and helps minimise side effects. Do not rush the titration schedule; allow your body adequate time to adjust at each dose level. If fatigue is particularly troublesome, discuss with your GP whether slowing the dose increase might be appropriate.
Lifestyle modifications can support energy levels. Prioritise good sleep hygiene, aiming for 7–9 hours of quality sleep nightly. Engage in regular physical activity appropriate to your fitness level—even light walking can improve energy and wellbeing. However, if you are experiencing significant caloric restriction, you may need to temporarily reduce exercise intensity whilst your body adapts.
Keep a symptom diary documenting when tiredness occurs, its severity, and any associated factors (meals, medication timing, activities). This information can help identify patterns and guide discussions with your healthcare team about potential adjustments to your treatment plan.
Whilst mild, transient tiredness during the initial weeks of GLP-1 treatment may be expected as your body adjusts, certain situations warrant prompt medical review. Contact your GP or diabetes care team if you experience any of the following:
Persistent or worsening fatigue that continues beyond the first 4–6 weeks of treatment or does not improve with dietary and lifestyle modifications
Severe tiredness that significantly impairs your ability to perform daily activities, work, or care for yourself
Symptoms suggestive of hypoglycaemia, particularly if occurring frequently or if you are unable to maintain blood glucose levels within target range
Signs of dehydration or electrolyte imbalance, including dizziness, reduced urine output, dark urine, persistent headaches, or muscle cramps
Concurrent symptoms such as unexplained weight loss beyond expected targets, persistent nausea or vomiting preventing adequate nutrition, or palpitations
Mood changes including low mood, anxiety, or depression, which can both cause and be exacerbated by fatigue
Snoring, witnessed pauses in breathing during sleep, or excessive daytime sleepiness, which may indicate obstructive sleep apnoea, a treatable condition common in people with obesity
Seek urgent medical attention (call 999 or go to A&E) if you experience severe chest pain, shortness of breath, or severe, persistent abdominal pain (especially if radiating to the back), as these could indicate serious conditions including pancreatitis, which is a rare but recognised complication of GLP-1 treatment.
Your GP may wish to perform investigations to exclude other causes of tiredness, which might include:
Blood tests: Full blood count (to check for anaemia), thyroid function tests, vitamin B12, folate and vitamin D levels, iron studies, renal and liver function, and HbA1c to assess overall glycaemic control. Coeliac screening may be considered if clinically indicated.
Review of concurrent medications to identify potential drug interactions or cumulative side effects
Assessment of nutritional intake and consideration of referral to a dietitian for specialist advice
In some cases, your healthcare team may recommend adjusting your GLP-1 dose, switching to an alternative GLP-1 medication, or modifying other diabetes medications to optimise your treatment whilst minimising side effects. Never stop or adjust your medication without medical guidance, as this could adversely affect your diabetes control or weight management goals. NICE guidance emphasises individualised treatment approaches, and your care plan should be tailored to balance therapeutic benefits with tolerability and quality of life.
If you suspect your medication is causing side effects, you can report these through the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or via the Yellow Card app).
Fatigue is classified as a common side effect of GLP-1 medications, affecting between 1 in 10 and 1 in 100 people. It occurs more frequently at higher doses used for weight management compared to lower doses prescribed for diabetes treatment.
Tiredness can result from reduced caloric intake due to appetite suppression, rapid weight loss, gastrointestinal symptoms causing dehydration and nutrient deficiencies, or hypoglycaemia when GLP-1 medications are combined with insulin or sulphonylureas.
Contact your GP if tiredness persists beyond 4–6 weeks, significantly impairs daily activities, is accompanied by frequent hypoglycaemia, signs of dehydration, unexplained weight loss, mood changes, or symptoms suggesting sleep apnoea such as excessive daytime sleepiness.
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