Janumet

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Janumet on Prescriptsy

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Janumet is a prescription-only combination medicine used to treat type 2 diabetes in adults. Each tablet contains sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, and metformin hydrochloride, a biguanide.

The two active ingredients work through complementary mechanisms to lower blood glucose levels. Janumet is prescribed when metformin alone does not achieve adequate blood sugar control.

It is manufactured by Merck Sharp and Dohme, available in two strengths (50 mg/850 mg and 50 mg/1000 mg), and is classified as a prescription-only medicine (POM) in the United Kingdom.

Type 2 diabetes is one of the most significant public health challenges facing the United Kingdom.

According to Diabetes UK, approximately 4.3 million people in the UK are living with a diabetes diagnosis, of whom around 90% have type 2.

A further estimated 850,000 people have type 2 diabetes but have not yet been diagnosed.

The condition arises when the body becomes resistant to the effects of insulin, or when the pancreas cannot produce enough insulin to meet demand, resulting in chronically elevated blood glucose.

Without effective management, high blood sugar damages blood vessels and nerves over time, leading to complications including heart disease, stroke, chronic kidney disease, retinopathy (eye damage), neuropathy (nerve damage), and foot problems that can lead to amputation.

This page provides a comprehensive clinical overview of Janumet, covering its mechanism of action, clinical evidence, dosage guidance, side effects, important safety warnings, and how to obtain a prescription in the United Kingdom.

Important safety information about Janumet

Before reading further, note these essential safety points about Janumet.

• Janumet is a prescription-only medicine and must be used under medical supervision.
• It must not be used in patients with type 1 diabetes, diabetic ketoacidosis, or severe kidney impairment (eGFR below 30).
• Regular kidney function tests are required during treatment.
• Metformin must be temporarily stopped before CT scans using iodinated contrast and before general anaesthesia.
• Seek immediate medical help if you develop severe persistent abdominal pain, as this may indicate pancreatitis.
• Temporarily stop Janumet during any acute illness causing dehydration.

Understanding type 2 diabetes

Type 2 diabetes develops when the body's cells become less responsive to insulin (insulin resistance) and the pancreatic beta cells cannot compensate by producing more insulin (relative insulin deficiency).

Insulin is the hormone that enables glucose from the bloodstream to enter cells, where it is used for energy.

When insulin action is impaired, glucose accumulates in the blood, producing hyperglycaemia.

Over time, persistent hyperglycaemia damages the lining of small and large blood vessels, increasing the risk of microvascular complications (retinopathy, nephropathy, neuropathy) and macrovascular complications (coronary heart disease, stroke, peripheral arterial disease).

The key risk factors for type 2 diabetes include obesity (particularly visceral adiposity), physical inactivity, a family history of diabetes, age over 40 (or over 25 in South Asian, Black African, and African-Caribbean populations), a history of gestational diabetes, and polycystic ovary syndrome.

The rising prevalence of type 2 diabetes in the UK is closely linked to increasing rates of obesity and sedentary lifestyles.

The management of type 2 diabetes follows a stepwise approach outlined by NICE guideline NG28.

Initial management centres on lifestyle modifications: a balanced diet emphasising whole grains, vegetables, lean protein, and healthy fats; regular physical activity (at least 150 minutes per week of moderate-intensity exercise); and weight loss for those who are overweight or obese.

When lifestyle measures alone are insufficient, metformin is recommended as the first-line pharmacological therapy.

If metformin monotherapy does not achieve the individual's HbA1c target (usually 48 mmol/mol or 53 mmol/mol, depending on circumstances), a second agent is added.

Sitagliptin is one of several options at this stage, alongside sulfonylureas, pioglitazone, SGLT2 inhibitors, and GLP-1 receptor agonists.

How Janumet works: mechanism of action

Janumet combines two medicines that target different aspects of the abnormal glucose metabolism seen in type 2 diabetes.

Metformin hydrochloride works primarily by suppressing hepatic glucose production. In type 2 diabetes, the liver often releases excessive glucose into the blood, particularly during fasting.

Metformin activates an intracellular enzyme called AMP-activated protein kinase (AMPK), which signals the liver to reduce gluconeogenesis (the manufacture of new glucose) and glycogenolysis (the breakdown of stored glycogen).

Metformin also enhances insulin sensitivity in peripheral tissues, particularly skeletal muscle, enabling cells to take up more glucose from the blood.

Additionally, metformin has a modest effect on delaying intestinal glucose absorption.

Importantly, metformin does not stimulate insulin secretion from the pancreas, which means it does not cause hypoglycaemia when used alone and is not associated with weight gain.

Sitagliptin is a highly selective inhibitor of the enzyme dipeptidyl peptidase-4 (DPP-4).

This enzyme normally breaks down the incretin hormones GLP-1 and GIP within minutes of their release from the gut after eating.

By blocking DPP-4, sitagliptin allows incretin levels to remain elevated for longer. GLP-1 stimulates insulin secretion and suppresses glucagon release from the pancreas, both in a glucose-dependent manner.

This means that sitagliptin enhances insulin secretion when blood glucose is elevated (after meals) but has little effect when glucose is normal, which is why it carries a low risk of hypoglycaemia.

GIP similarly augments insulin secretion in response to food intake.

The combination of metformin and sitagliptin addresses at least three of the major pathophysiological defects in type 2 diabetes: excessive hepatic glucose output (metformin), reduced peripheral glucose uptake (metformin), and impaired incretin-mediated insulin secretion (sitagliptin).

This complementary approach typically produces greater HbA1c reduction than either component alone.

Clinical evidence and UK prescribing guidance

The efficacy and safety of the sitagliptin-metformin combination have been evaluated in a substantial body of clinical trial evidence.

In pivotal studies, adding sitagliptin to metformin monotherapy reduced HbA1c by an additional 0.6 to 0.7 percentage points (approximately 6 to 8 mmol/mol) compared with continuing metformin alone.

The combination was weight-neutral and had a low rate of hypoglycaemia comparable to metformin monotherapy.

NICE guideline NG28 recommends offering a DPP-4 inhibitor (such as sitagliptin) as one option for dual therapy alongside metformin when metformin alone does not achieve the HbA1c target.

The choice among second-line agents depends on individual factors including the patient's cardiovascular risk profile, weight, risk of hypoglycaemia, and personal preference.

SGLT2 inhibitors are increasingly favoured for patients with established cardiovascular disease or heart failure because of their proven cardiovascular and renal protective benefits.

However, DPP-4 inhibitors remain an appropriate choice for many patients, particularly those who prioritise a low risk of hypoglycaemia and weight gain, and who do not have indications for an SGLT2 inhibitor or GLP-1 receptor agonist.

The TECOS (Trial Evaluating Cardiovascular Outcomes with Sitagliptin) study demonstrated that sitagliptin did not increase the risk of major adverse cardiovascular events compared with placebo in patients with type 2 diabetes and established cardiovascular disease.

This cardiovascular safety data, combined with the agent's favourable side effect profile, supports the continued use of sitagliptin in appropriate clinical settings.

Janumet compared with other combination diabetes medicines

Several combination tablets pairing a DPP-4 inhibitor with metformin are available in the UK. Jentadueto (linagliptin/metformin), Eucreas (vildagliptin/metformin), and Komboglyze (saxagliptin/metformin) are alternatives to Janumet.

The DPP-4 inhibitors in these products have broadly similar efficacy in terms of HbA1c reduction, but they differ in their pharmacokinetic properties and dose adjustments in renal impairment.

Linagliptin, for example, does not require dose adjustment in renal impairment because it is primarily eliminated through the bile rather than the kidneys.

The metformin component, however, still requires renal function monitoring regardless of which DPP-4 inhibitor is used.

SGLT2 inhibitor-metformin combinations (such as empagliflozin/metformin and dapagliflozin/metformin) offer additional benefits including weight loss, blood pressure reduction, and cardiovascular and renal protection, making them increasingly preferred as second-line add-on therapy for patients with relevant comorbidities.

GLP-1 receptor agonists (such as liraglutide and semaglutide) produce greater HbA1c reduction and weight loss than DPP-4 inhibitors but are administered by injection (or orally in the case of oral semaglutide) and are generally reserved for patients who need intensified therapy.

Dosage and administration

Janumet is taken twice daily with meals, one tablet with breakfast and one with the evening meal. The tablets should be swallowed whole with water.

Two strengths are available: 50 mg sitagliptin/850 mg metformin and 50 mg sitagliptin/1000 mg metformin.

The choice of strength is determined by the dose of metformin the patient was taking before switching to Janumet, or by the dose tolerated during titration.

The total daily dose of sitagliptin in Janumet is 100 mg, which is the standard therapeutic dose.

Renal function monitoring is essential.

Check eGFR before starting treatment, annually in patients with normal renal function, and every 3 to 6 months in patients over 65 or with declining renal function.

Janumet should not be initiated if eGFR is below 45 mL/min/1.73 m2, and must be stopped if eGFR falls below 30.

In patients with moderate renal impairment (eGFR 30 to 44), metformin doses above 1000 mg per day are not recommended, and individual component tablets should be used if needed.

In acute illness involving dehydration, fever, or reduced fluid intake, temporarily stop Janumet and seek medical advice. Restart only when you are fully recovered and your kidney function has been confirmed as stable.

Side effects of Janumet

Gastrointestinal effects

The most commonly reported side effects of Janumet are gastrointestinal and attributable to metformin: nausea, vomiting, diarrhoea, abdominal pain or discomfort, bloating, flatulence, and metallic taste.

These effects typically occur at the start of treatment or following a dose increase and often diminish over several weeks.

Taking the tablets with food and ensuring gradual dose escalation minimise these symptoms.

If gastrointestinal side effects persist, your prescriber may consider reducing the dose or switching to a modified-release metformin preparation.

Other common side effects

Upper respiratory tract infections, nasopharyngitis, and headache have been reported with sitagliptin at rates similar to placebo. Dizziness and constipation are uncommon but recognised.

Hypoglycaemia is rare when Janumet is used alone or with medicines that do not stimulate insulin secretion.

When Janumet is combined with a sulfonylurea or insulin, episodes of mild to moderate hypoglycaemia may occur and should be managed by adjusting the dose of the sulfonylurea or insulin.

Rare and serious side effects

Pancreatitis has been reported in patients taking DPP-4 inhibitors, including sitagliptin.

The absolute risk is low, but patients should be aware of the symptoms: severe, persistent abdominal pain, often radiating to the back, sometimes accompanied by nausea and vomiting.

If pancreatitis is suspected, stop Janumet immediately and seek emergency care (call 999 or attend A&E).

Lactic acidosis is an extremely rare but life-threatening complication associated with metformin, occurring almost exclusively in patients with predisposing factors such as severe renal impairment, hepatic failure, dehydration, sepsis, or excessive alcohol consumption.

Symptoms include nausea, vomiting, rapid or laboured breathing, abdominal pain, drowsiness, and muscle cramps. This requires immediate emergency treatment.

Bullous pemphigoid, a rare blistering skin condition, has been reported with DPP-4 inhibitors. Severe allergic reactions, including anaphylaxis and angioedema, are very rare.

Long-term metformin use may lead to vitamin B12 deficiency, presenting as anaemia, fatigue, or peripheral neuropathy (tingling or numbness in hands and feet).

When to seek urgent help

Contact your GP or call NHS 111 if you develop persistent gastrointestinal symptoms, unexplained fatigue, tingling in your extremities, or skin blistering.

Call 999 or attend A&E if you experience severe abdominal pain, difficulty breathing, rapid breathing, muscle cramps with drowsiness, swelling of the face or throat, or signs of a severe low blood sugar episode that does not respond to glucose.

Report suspected adverse reactions to the MHRA at yellowcard.mhra.gov.uk .

Warnings and precautions

Contraindications

Janumet must not be used in patients with type 1 diabetes or diabetic ketoacidosis.

It is contraindicated in severe renal impairment (eGFR below 30), hepatic insufficiency, conditions predisposing to lactic acidosis (including decompensated heart failure, respiratory failure, and recent myocardial infarction), and known hypersensitivity to either active ingredient or any excipient.

Monitoring

Renal function (eGFR) must be checked before starting treatment and at least annually thereafter.

HbA1c should be measured every 3 to 6 months to assess glycaemic control and guide treatment decisions.

Vitamin B12 levels should be checked periodically, particularly in patients who develop symptoms suggestive of deficiency. Liver function should be assessed if clinically indicated.

Drug interactions

Cimetidine may increase metformin plasma levels by competing for renal tubular secretion. Glucocorticoids, sympathomimetics, and thyroid hormones may raise blood glucose and reduce the effectiveness of Janumet.

Loop and thiazide diuretics may impair renal function and increase the risk of metformin accumulation. ACE inhibitors may enhance the blood glucose-lowering effect slightly.

Alcohol potentiates the risk of lactic acidosis with metformin.

Pregnancy and breastfeeding

Janumet should not be used during pregnancy or breastfeeding.

Women with type 2 diabetes who are planning a pregnancy or who become pregnant should be switched to insulin under specialist guidance.

Metformin may be considered as part of gestational diabetes management, but the combination product Janumet is not appropriate for use during pregnancy.

Sick day rules

In any acute illness causing dehydration (vomiting, diarrhoea, high fever, reduced oral intake), temporarily stop Janumet and contact your GP or diabetes team.

Dehydration increases the risk of acute kidney injury and lactic acidosis.

Resume Janumet only once you are eating and drinking normally and your kidney function is confirmed as stable.

Your diabetes team should provide you with personalised sick day rules.

How to get Janumet in the UK

Janumet is a prescription-only medicine. Your GP, diabetologist, or an authorised online prescriber registered with the General Pharmaceutical Council (GPhC) can prescribe it after a clinical assessment.

The NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

All patients with diabetes in England are entitled to a medical exemption certificate (available through your GP), which entitles you to free prescriptions for all medicines, not just diabetes treatment.

Living with type 2 diabetes: lifestyle alongside Janumet

Medication is one part of a comprehensive approach to managing type 2 diabetes.

NICE recommends combining drug therapy with sustained lifestyle changes for optimal glycaemic control and cardiovascular risk reduction.

Aim for a balanced diet based on whole grains, vegetables, lean protein, healthy fats, and limited refined sugars and processed foods.

Regular physical activity, at least 150 minutes per week of moderate-intensity exercise such as brisk walking, cycling, or swimming, improves insulin sensitivity and helps maintain a healthy weight.

If you are overweight, losing even 5 to 10% of your body weight can meaningfully improve blood sugar control.

Limit alcohol to no more than 14 units per week. Stop smoking if applicable, as smoking significantly increases cardiovascular risk in people with diabetes.

Self-monitoring of blood glucose may be recommended by your diabetes team, particularly if you are at risk of hypoglycaemia or during dose adjustments.

Keep all follow-up appointments, including annual diabetes reviews, retinal screening, and foot checks.

Managing blood pressure and cholesterol alongside blood sugar is essential for reducing the overall risk of diabetes-related complications.

Sources

• Janumet, Summary of Product Characteristics (EMC)
• Sitagliptin with metformin, British National Formulary (BNF)
• NICE NG28: Type 2 diabetes in adults: management
• Type 2 diabetes, NHS
• Diabetes UK
• MHRA Yellow Card Scheme