Many patients prescribed GLP-1 receptor agonists for type 2 diabetes or weight management wonder whether these medications might weaken their immune defences. This concern is understandable, particularly as these treatments become more widely used. Current evidence provides reassuring answers: GLP-1 receptor agonists do not suppress the immune system in the way that immunosuppressive drugs do. In fact, emerging research suggests they may have anti-inflammatory properties. This article examines the scientific evidence, addresses infection-related considerations, and explains when to seek medical advice whilst taking these medications.

What Are GLP-1 Receptor Agonists and How Do They Work?

Glucagon-like peptide-1 (GLP-1) receptor agonists are a class of medications primarily used to manage type 2 diabetes mellitus and, more recently, obesity. These medicines include semaglutide (Ozempic, Wegovy), dulaglutide (Trulicity), liraglutide (Victoza, Saxenda), and exenatide (Byetta, Bydureon). They work by mimicking the action of naturally occurring GLP-1, a hormone produced in the intestine in response to food intake.

The mechanism of action involves several complementary pathways. GLP-1 receptor agonists stimulate insulin secretion from pancreatic beta cells in a glucose-dependent manner, meaning they promote insulin release only when blood glucose levels are elevated. This reduces the risk of hypoglycaemia compared with some other diabetes medications, although this risk increases when combined with insulin or sulfonylureas. Simultaneously, these agents suppress glucagon secretion from pancreatic alpha cells, further helping to lower blood glucose levels. They also slow gastric emptying, which prolongs the feeling of fullness after meals and contributes to weight loss.

Additionally, GLP-1 receptor agonists act on appetite centres in the brain, particularly the hypothalamus, reducing hunger and food intake. This dual benefit on glycaemic control and weight management has made them increasingly popular therapeutic options. According to NICE guidance (NG28), GLP-1 receptor agonists are recommended for adults with type 2 diabetes who have not achieved adequate glycaemic control with metformin and other oral agents, or as part of combination therapy in specific clinical circumstances. Treatment should only continue if there is a reduction in HbA1c of at least 11 mmol/mol (1.0%) and weight loss of at least 3% of initial body weight after 6 months.

These medications are administered via subcutaneous injection, with dosing frequencies ranging from twice daily to once weekly depending on the specific formulation. Understanding how GLP-1 receptor agonists work provides important context when considering their broader effects on bodily systems, including potential impacts on immune function.

Research Evidence on GLP-1 and Immune Function

The question of whether GLP-1 receptor agonists lower immune system function is one that concerns many patients, particularly given the increasing use of these medications. Current evidence does not support the notion that GLP-1 receptor agonists suppress or weaken the immune system in the way that immunosuppressive medications (such as corticosteroids or disease-modifying antirheumatic drugs) do.

Interestingly, emerging research suggests that GLP-1 receptor agonists may have anti-inflammatory properties rather than immunosuppressive effects. Laboratory studies have demonstrated that GLP-1 receptors are expressed on various immune cells, including macrophages, lymphocytes, and monocytes. Activation of these receptors appears to modulate inflammatory responses, potentially reducing excessive inflammation without compromising the body's ability to fight infections. Some studies have shown reductions in inflammatory markers such as C-reactive protein (CRP) and interleukin-6 (IL-6) in patients treated with GLP-1 receptor agonists, though these findings are preliminary and not an indication for use.

Clinical trials examining cardiovascular outcomes in patients taking GLP-1 receptor agonists have not identified increased rates of serious infections compared with placebo groups. The SUSTAIN-6 and LEADER trials, which followed thousands of patients over several years, did not report immune system suppression as an adverse effect. However, it is important to note that these trials were not specifically designed to assess immune function comprehensively.

There is no official link established between GLP-1 receptor agonists and immunosuppression according to regulatory bodies including the MHRA and EMA. The Summary of Product Characteristics (SmPC) for these medications does not list immune system suppression among recognised adverse effects. It should be noted, however, that rare hypersensitivity reactions can occur. Patients should be reassured that taking a GLP-1 receptor agonist for diabetes or weight management does not mean their immune defences are being deliberately weakened, unlike with medications specifically designed to suppress immune responses.

Infection Risk and GLP-1 Treatment: What Patients Should Know

Whilst GLP-1 receptor agonists do not suppress the immune system, patients should be aware of specific infection-related considerations associated with these medications. The most commonly reported infection concern relates to the gastrointestinal tract, given that these drugs slow gastric emptying and affect gut motility.

Common adverse effects of GLP-1 receptor agonists include nausea, vomiting, diarrhoea, and constipation, which occur in a significant proportion of patients, particularly during dose escalation. These gastrointestinal symptoms are not infections but can occasionally be confused with gastroenteritis. Patients experiencing persistent vomiting or diarrhoea should maintain adequate hydration and contact their GP if symptoms are severe or prolonged, as dehydration can complicate diabetes management. If you are unable to keep fluids down, you may need to temporarily pause your GLP-1 treatment until you recover, following advice from your healthcare team.

There have been rare reports of pancreatitis (inflammation of the pancreas) in patients taking GLP-1 receptor agonists, though a definitive causal relationship remains uncertain. Symptoms include severe, persistent abdominal pain that may radiate to the back, often accompanied by nausea and vomiting. If pancreatitis is suspected, you should discontinue the GLP-1 medication immediately and seek urgent medical assessment. Additionally, some patients may experience injection site reactions, including redness, itching, or swelling, which should be distinguished from cellulitis or other skin infections.

GLP-1 receptor agonists have also been associated with an increased risk of gallbladder disease, including gallstones and inflammation of the gallbladder. Symptoms may include pain in the upper right abdomen, fever, or yellowing of the skin or eyes (jaundice), requiring prompt medical attention.

Regarding respiratory and urinary tract infections, large-scale clinical trials have not demonstrated increased susceptibility in patients taking GLP-1 receptor agonists compared with control groups. Patients with diabetes are generally at higher risk of certain infections due to elevated blood glucose levels impairing immune cell function, but improved glycaemic control achieved with GLP-1 therapy may actually reduce this baseline infection risk.

Patient safety advice includes:

• Maintaining good injection technique and site rotation to minimise local reactions

• Staying up to date with routine vaccinations, including annual influenza and pneumococcal vaccines as recommended for people with diabetes

• Monitoring for signs of infection and seeking prompt medical advice if concerned

• Following 'sick day rules' during illness – maintain hydration, continue medication if possible, but temporarily pause GLP-1 treatment if unable to keep fluids down

• Reporting suspected side effects via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app)

Patients should not discontinue their GLP-1 receptor agonist due to concerns about immune function without first consulting their prescribing clinician.

When to Speak with Your GP About GLP-1 and Immunity

Whilst GLP-1 receptor agonists are generally well-tolerated and do not compromise immune function, there are specific circumstances when patients should contact their GP or healthcare team for guidance and reassurance.

You should arrange a routine appointment if you:

• Experience recurrent infections (such as urinary tract infections, respiratory infections, or skin infections) after starting GLP-1 therapy, even though there is no established causal link

• Have concerns about your overall health or notice unexplained symptoms such as persistent fatigue, unexplained weight loss beyond expected therapeutic effect, or night sweats

• Are planning to start immunosuppressive medication for another condition and want to discuss potential interactions

• Are due for vaccinations and wish to confirm these are safe to receive whilst taking a GLP-1 receptor agonist (they are, and should be encouraged)

• Experience persistent gastrointestinal symptoms that interfere with nutrition, hydration, or quality of life

• Are approaching your 6-month review, when your GP will assess whether you've met the NICE continuation criteria (HbA1c reduction ≥11 mmol/mol and weight loss ≥3% of initial body weight)

You should seek urgent medical attention if you develop:

• Severe, persistent abdominal pain, particularly if radiating to the back (possible pancreatitis) – stop taking your GLP-1 medication immediately

• Signs of severe dehydration due to vomiting or diarrhoea, including dizziness, reduced urine output, or confusion

• Symptoms of a serious infection such as high fever (>38°C), rigors, difficulty breathing, or altered consciousness

• Spreading redness, warmth, and swelling around injection sites that might indicate cellulitis

• Symptoms of diabetic ketoacidosis, which can occur in the context of acute illness (though rare with GLP-1 monotherapy) – if you're also taking insulin or SGLT2 inhibitors, check ketones during illness and seek urgent help if elevated

• Signs of a severe allergic reaction including swelling of the face, lips or tongue, or difficulty breathing – call 999 immediately

• Pain in the upper right abdomen, fever, or yellowing of the skin/eyes, which could indicate gallbladder problems

NICE guidance (NG28) recommends regular monitoring of patients on GLP-1 receptor agonists, typically including review of glycaemic control, weight, gastrointestinal tolerability, and overall treatment response every 3–6 months. These appointments provide an opportunity to discuss any concerns about infections or immune health. Your GP can arrange appropriate investigations if clinically indicated, such as full blood count, inflammatory markers, or HbA1c testing.

It is important to maintain open communication with your healthcare team. If you have read information suggesting GLP-1 medications affect immunity, discuss this directly with your GP or diabetes specialist nurse, who can provide evidence-based reassurance and address your individual circumstances. Remember that well-controlled diabetes itself supports better immune function, and GLP-1 receptor agonists contribute positively to achieving this goal.

Frequently Asked Questions