Understanding how Ozempic works in the body is essential for patients and healthcare professionals managing type 2 diabetes. Ozempic (semaglutide) is a glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for improving blood sugar control in adults with type 2 diabetes mellitus. Administered as a once-weekly injection, it mimics natural hormones to regulate glucose levels, slow digestion, and reduce appetite. This article explores the mechanisms through which Ozempic exerts its therapeutic effects, including glucose-dependent insulin secretion, glucagon suppression, delayed gastric emptying, and central appetite regulation. We also examine who can safely use Ozempic, expected timelines for clinical effects, and important safety considerations aligned with UK guidance from NICE, the MHRA, and the BNF.

What Is Ozempic and What Does It Treat?

Ozempic is the brand name for semaglutide, a prescription medicine licensed in the UK for the treatment of type 2 diabetes mellitus in adults. It belongs to a class of medications known as glucagon-like peptide-1 (GLP-1) receptor agonists. Ozempic is administered as a once-weekly subcutaneous injection, typically into the abdomen, thigh, or upper arm, and is available in pre-filled pen devices at doses of 0.25 mg, 0.5 mg, 1 mg, and 2 mg.

The primary indication for Ozempic is to improve glycaemic control (blood sugar levels) in adults with type 2 diabetes when diet and exercise alone are insufficient. It is often prescribed alongside other glucose-lowering medications such as metformin, sulfonylureas, or insulin, depending on individual patient needs. According to NICE guideline NG28, GLP-1 receptor agonists like Ozempic may be considered as a third-line treatment option when a person has a BMI of 35 kg/m² or higher (adjusted for ethnicity) and specific psychological or medical problems associated with obesity, or a BMI lower than 35 kg/m² and insulin would have significant occupational implications or weight loss would benefit other significant obesity-related comorbidities.

Whilst Ozempic has gained attention for its effects on weight loss, it is important to note that in the UK, it is not licensed for weight management alone. A related formulation of semaglutide, marketed as Wegovy, is specifically licensed for chronic weight management in certain patient groups. Ozempic should only be used under medical supervision for its approved indication of type 2 diabetes, and prescribing decisions should be made by a qualified healthcare professional following a comprehensive assessment of the patient's medical history and treatment goals.

Ozempic is not recommended for use in children and adolescents under 18 years of age as safety and efficacy have not been established in this population.

How Long Does Ozempic Take to Work?

The timeframe for Ozempic to demonstrate clinical effects varies depending on the outcome being measured. Blood sugar control begins to improve shortly after starting treatment, with glycaemic effects observed from the first doses. Measurable reductions in fasting plasma glucose typically occur within the first few weeks, with steady-state plasma concentrations achieved after approximately 4 to 5 weeks of consistent use.

The full therapeutic effect on glycaemic control, as reflected by HbA1c (a marker of average blood glucose over the preceding 2–3 months), generally becomes apparent after approximately 8 to 12 weeks of consistent use. HbA1c reductions typically range from 11-22 mmol/mol (1-2%), depending on baseline levels and individual response.

Patients often notice appetite suppression and early satiety within the first 1 to 2 weeks of starting Ozempic, which may contribute to gradual weight reduction. Weight loss tends to occur progressively over several months, with most patients experiencing a reduction of approximately 3-6% of baseline body weight within the first 6 months of therapy, though individual responses vary considerably.

It is essential to follow the recommended dose escalation schedule to minimise gastrointestinal side effects and allow the body to adjust. Treatment usually begins with a starting dose of 0.25 mg once weekly for 4 weeks, followed by an increase to 0.5 mg. Further dose increases to 1 mg or 2 mg may be considered based on glycaemic response and tolerability.

According to NICE guidance, GLP-1 receptor agonist treatment should only be continued if a person has a beneficial metabolic response (a reduction of at least 11 mmol/mol [1%] in HbA1c and a weight loss of at least 3% of initial body weight in 6 months).

If you miss a dose, take Ozempic as soon as possible within 5 days after the missed dose. If more than 5 days have passed, skip the missed dose and take your next dose on the regularly scheduled day.

Patients should maintain realistic expectations about the gradual nature of improvements in blood sugar control and weight. Regular monitoring by a healthcare professional, including HbA1c measurements and assessment of treatment response, is crucial to optimise outcomes.

Who Should Not Use Ozempic?

Ozempic is contraindicated in patients with a history of severe hypersensitivity to semaglutide or any of the excipients in the product. Hypersensitivity reactions, though rare, can include anaphylaxis and angioedema.

Whilst animal studies have shown an association between GLP-1 receptor agonists and thyroid C-cell tumours, the relevance to humans is uncertain. The UK product information notes this preclinical finding but does not list a history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2) as formal contraindications. However, patients with these conditions should discuss the potential risks and benefits with their healthcare provider.

Ozempic is not recommended for individuals with type 1 diabetes or for the treatment of diabetic ketoacidosis, as it is not a substitute for insulin in these contexts. It is also not indicated for use in children and adolescents under 18 years of age.

Caution is advised in patients with a history of pancreatitis, as GLP-1 receptor agonists have been associated with acute pancreatitis in some cases. Patients should be counselled to seek immediate medical attention if they experience persistent severe abdominal pain. Similarly, Ozempic has been associated with gallbladder disorders, including cholelithiasis and cholecystitis. Patients should be advised to report symptoms such as right upper abdominal pain, fever, nausea and vomiting.

Patients with diabetic retinopathy should be monitored closely, as rapid improvements in glucose control have been associated with temporary worsening of retinopathy. Regular eye examinations are recommended, particularly during the initial phase of treatment.

When Ozempic is used in combination with a sulfonylurea or insulin, there is an increased risk of hypoglycaemia. Dose reduction of these medications may be necessary when starting Ozempic. Patients should be educated about the signs and symptoms of hypoglycaemia and how to manage it.

Ozempic should be used with caution in individuals with severe gastrointestinal disease, including gastroparesis, as it slows gastric emptying and may exacerbate symptoms. The gastrointestinal side effects of Ozempic can lead to dehydration in some patients, which may cause acute kidney injury. Patients should maintain adequate fluid intake, especially if experiencing vomiting or diarrhoea.

Regarding pregnancy and breastfeeding, Ozempic should be avoided during pregnancy and discontinued at least 2 months before a planned pregnancy due to its long half-life. It is not recommended during breastfeeding as there is insufficient data on the excretion of semaglutide in human milk. Women of childbearing potential should use effective contraception during treatment.

Patients with severe renal impairment or hepatic impairment should be monitored closely, though dose adjustment is not routinely required.

Patients taking warfarin or other coumarin derivatives should have their INR monitored when initiating Ozempic treatment, as cases of increased INR have been reported.

If you experience any side effects, talk to your doctor, pharmacist or nurse. This includes any possible side effects not listed in the patient information leaflet. You can also report side effects directly via the Yellow Card Scheme at yellowcard.mhra.gov.uk or search for MHRA Yellow Card in the Google Play or Apple App Store.

How Does Ozempic Work in the Body?

Ozempic exerts its therapeutic effects through multiple complementary mechanisms that target the underlying pathophysiology of type 2 diabetes. As a GLP-1 receptor agonist, semaglutide mimics the action of naturally occurring glucagon-like peptide-1, an incretin hormone produced by intestinal L-cells in response to food intake. The medication has been structurally modified to resist degradation by the enzyme dipeptidyl peptidase-4 (DPP-4), resulting in a prolonged half-life of approximately one week, which enables once-weekly dosing.

The primary mechanism involves glucose-dependent insulin secretion. When blood glucose levels are elevated, Ozempic binds to GLP-1 receptors on pancreatic beta cells, stimulating the release of insulin. Crucially, this effect is glucose-dependent, meaning insulin secretion diminishes as blood glucose normalises, thereby reducing the risk of hypoglycaemia compared to some other diabetes medications. Simultaneously, Ozempic suppresses glucagon secretion from pancreatic alpha cells. Glucagon normally raises blood glucose by promoting hepatic glucose production; its suppression helps prevent excessive glucose release from the liver.

Ozempic also significantly affects gastric emptying, slowing the rate at which food moves from the stomach into the small intestine. This delay reduces the speed of glucose absorption after meals, contributing to improved postprandial (after-eating) glucose control. Additionally, this mechanism promotes feelings of fullness and satiety, which helps reduce overall caloric intake. It's worth noting that this gastric-emptying effect is most pronounced early in treatment and may diminish somewhat with continued therapy.

Central nervous system effects play an important role in Ozempic's action. GLP-1 receptors are present in appetite-regulating centres of the brain, particularly the hypothalamus. Activation of these receptors reduces appetite and food cravings, leading to decreased energy intake and progressive weight loss. This effect on appetite regulation is thought to be mediated through both direct central actions and indirect signals from the gastrointestinal tract.

The combined effects of enhanced insulin secretion, reduced glucagon release, delayed gastric emptying, and appetite suppression work synergistically to improve glycaemic control and promote weight reduction. Clinical studies have demonstrated that Ozempic can reduce HbA1c by approximately 11-22 mmol/mol (1-2%) on average, with many patients also experiencing weight loss of about 3-6% of baseline body weight. These multifaceted mechanisms make Ozempic a valuable option in the management of type 2 diabetes, particularly for patients who would benefit from concurrent weight management. However, individual responses vary, and treatment should always be personalised under medical supervision with regular monitoring of efficacy and tolerability.

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