Weight loss injections UK: A complete guide to options, effectiveness and safety

As of June 2025, the most recent data shows that 64% of people in the UK live with being overweight or obese.

Carrying excess body fat leads to increased health risks such as type 2 diabetes, organ dysfunction, sexual health problems, mental health problems and even various cancers.

To combat these risks, at least 500,000 people in the UK are taking prescription weight loss injections like semaglutide or tirzepatide.

The results of these medical weight loss treatments are astonishing, with people losing a high percentage of body weight and experiencing significant improvements in overall health.

But while these slimming injections are available through the NHS, supplies are limited and national rollout is slow.

That’s why 95% of people undergoing treatment with prescription weight loss injections get their medications privately through services like The Online Clinic.

As a UK licensed and regulated clinic with over 20 years’ experience, The Online Clinic offers prescriptions for weight loss injections following a thorough medical health review.

Register as a patient today to request a trusted prescription for weight loss injections in the UK.

How do weight loss injections work?

GLP-1 receptor agonists

The most popular UK weight loss injections are glucagon-like peptide-1 (GLP-1) receptor agonist medications.

GLP-1 is a hormone that your body releases when you eat to:

• Trigger insulin release: Insulin is a hormone that makes your cells store blood glucose (sugar) as glycogen for later use. This helps control extreme peaks and crashes in blood sugar
• Block glucagon secretion: The hormone glucagon tells your liver to release stored glucose into the bloodstream. Blocking this hormone helps in keeping your blood sugar stable.
• Slow digestion: GLP-1 increases the time it takes for food to move through your digestive system, which keeps you feeling fuller for longer
• Increase satiety: By binding to receptors in the brain, GLP-1 sends signals that you’re no longer hungry

GLP-1 agonists mimic this hormone. So with GLP-1 agonist injections, you can benefit from controlled blood sugar and appetite regulation even without eating.

This makes it easier to take in fewer calories, burn more and lose weight.

GIP receptor agonists

One prescription weight loss medication, Mounjaro, has dual GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist effects.

Clinical trials suggest that GIP enhances the effects of GLP-1.

That’s because GIP works to:

• Boost insulin sensitivity: This hormone improves insulin function in fat tissue, helping to keep blood sugar stable and prevent crashes that drive excess eating
• Regulate appetite: Like GLP-1, GIP binds to hormone receptors in the brain to reduce feelings of hunger
• Improve fat burning: Evidence suggests that GIP alters fat metabolism, signalling your body to burn fat rather than store it
• Fight inflammation: GIP may reduce inflammation in fat tissue, leading to improvements in overall metabolic health

This can help you lose more weight and further reduce your risk of heart, kidney and fatty liver disease.

You can access GLP-1 and dual GIP/GLP-1 slimming injections online with The Online Clinic even without an NHS prescription.

Register online and complete a short medical health questionnaire for convenient access to UK weight loss injections.

Types of weight loss injections in the UK

Saxenda (liraglutide)

Saxenda is a GLP-1 agonist medication with the active ingredient liraglutide.

It helps regulate appetite and food intake by increasing satiety and slowing gastric emptying.

Patients take a daily injection using a pre-filled pen.

At the lowest dose, one pen will last for around 17 days. At the highest, it’ll last for around six days.

Doses of Saxenda start at 0.6 mg daily. This increases by 0.6 mg every week up to a maximum dose of 3 mg.

Is Saxenda effective?

A randomised controlled trial of 3 mg of liraglutide in weight management studied the weight loss effects of the active ingredient in 3,371 adults over 56 weeks.

Participants had a body mass index (BMI) of 30 or greater, or of 27 or greater with at least one weight-related comorbidity. None were diagnosed with diabetes.

Whether taking liraglutide or a placebo, participants also received a reduced-calorie diet and physical activity counselling.

At the end of the study, participants taking liraglutide had lost an average of 8.4 kg compared to 2.8 kg in the placebo control group.

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Ozempic (semaglutide)

Ozempic is a semaglutide GLP-1 agonist slimming injection.

It works like Saxenda to reduce appetite and improve blood sugar control. But it’s longer lasting, so you only need a weekly injection using a prefilled pen.

Ozempic pens are multiuse, containing four maintenance doses.

Doses start at 0.25 mg for four weeks, then increase to 0.5 mg for at least four weeks.

Doses of 1 mg and 2 mg are available for patients who need additional blood sugar control. This could be those with chronic kidney disease or whose A1C needs shift as their type 2 diabetes changes.

However, due to past shortages, Ozempic isn’t approved for weight loss in the UK.

Instead, it’s reserved only for controlling blood sugar in people with type 2 diabetes.

Is Ozempic effective?

The manufacturer of Ozempic, Novo Nordisk, reports average weight loss of 14 lbs in patients taking Ozempic 2 mg for 40 weeks.

Clinical trial data specifically testing Ozempic for weight loss is limited. But other clinical trials have been conducted on the active ingredient semaglutide, also present in Wegovy.

Wegovy (semaglutide)

Like Ozempic, Wegovy is a GLP-1 agonist medication that uses semaglutide to suppress appetite, increase satiety and slow digestion.

However, it uses a higher maximum dose.

Wegovy weekly injections are administered using a prefilled pen containing four prescribed doses.

Patients start with a dose of 0.25 mg for four weeks. This is increased to 0.5 mg and then 1 mg for four weeks each, with a final ongoing dose of either 1.7 mg or 2.4 mg a week depending on your needs.

Wegovy is prescribed for a maximum of two years.

Is Wegovy effective?

The Semaglutide Treatment Effects in People with Obesity (STEP) trials studied the effect of 2.4 mg semaglutide (the same dose as Wegovy) on 1,961 adults for 68 weeks.

Similar to the liraglutide trials, participants had a BMI of 30 or greater, or of 27 or greater in those with at least one weight-related co-existing condition. None were diagnosed with diabetes.

All participants, whether taking semaglutide or a placebo, also used a calorie-reduced diet and increased physical exercise.

Those taking semaglutide lost an average of 15.3 kg (14.9% of total body weight) compared to 2.6 kg (2.4%) in the placebo control group.

This shows that semaglutide slimming injections like Wegovy have a significant effect on weight loss compared to diet and exercise alone.

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Mounjaro (tirzepatide)

Most weight loss injections rely only on GLP-1 agonism.

But Mounjaro, with the active ingredient tirzepatide, combines GLP-1 appetite suppression with the enhanced insulin sensitivity of GIP for greater weight loss results.

Patients receive weekly injections using a single-use pen.

Doses start at 2.5 mg, increasing by 2.5 mg every four weeks up to a maximum of 15 mg.

Is Mounjaro effective?

In tests of Mounjaro vs Ozempic, manufacturers Eli Lilly and Company report an average weight loss of 25 lbs in those taking Mounjaro 15 mg for 40 weeks.

This data is supported by other clinical trials.

The SURMOUNT trials observed 2,539 participants taking weekly doses of 5 mg, 10 mg or 15 mg of tirzepatide over 72 weeks.

94.5% of participants had a BMI of 30 or higher, and none had diabetes.

At the end of the trial, participants displayed greater average weight loss with higher doses of tirzepatide:

These results suggest that dual GIP/GLP-1 agonist slimming injections have a significantly greater impact on weight loss compared to other options.

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Comparison of weight loss injections in the UK

Are UK weight loss injections safe?

Each prescription weight loss injection has its own side effects and risks.

But some are shared between medications.

Common side effects of slimming injections include:

• Loss of appetite
• Nausea
• Vomiting
• Diarrhoea
• Indigestion
• Stomach issues

These are usually mild to moderate, and typically occur when increasing dosage.

However, they tend to improve quickly as your body gets used to the medication.

While rare, some patients can experience more serious side effects such as:

• Severe allergic reactions (anaphylaxis)
• Pancreatitis
• Kidney damage
• Hypoglycaemia (low blood sugar)
• Worsening diabetic retinopathy

If you experience any serious side effects, seek immediate medical attention.

Who’s eligible for prescription weight loss injections?

According to NHS obesity treatment guidelines, weight loss injections in the UK should only be prescribed for those with:

• A BMI of 35 or more
• A BMI of 32.5 or more for those of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean origin

You can check your BMI using our online BMI calculator.

On top of this, Saxenda (liraglutide) isn’t prescribed for those with non-diabetic hyperglycaemia (high blood sugar) or high risk of heart problems.

And Mounjaro (trizepatide) is generally only prescribed for those with at least one weight-related health problem, such as type 2 diabetes or obstructive sleep apnoea.

Why are prescription weight loss eligibility criteria so strict?

The NHS has strict eligibility criteria because they have limited supplies of weight loss injections because of funding constraints.

However, private pharmacies and clinics like The Online Clinic have better access to these medications as patients pay for treatment.

That means we can prescribe them under less strict criteria (but still within the terms of the licence), allowing more people to access these life-changing drugs.

Despite lower eligibility criteria, we still carry out a thorough health check to ensure the benefits of taking prescription weight loss medication significantly outweigh the risks.

Register as a patient today to see if you’re eligible for weight loss injections in the UK.

The importance of medical supervision and avoiding unregulated providers

As with any medication it’s important to undergo prescription weight loss treatment under medical supervision from a regulated healthcare provider.

This ensures that you benefit from:

• Medical assessment: Not everyone is a suitable candidate for weight loss injections. A qualified doctor will assess your medical health profile and risk factors before prescribing medication
• Proper dosages: These medications require gradual dose escalation to minimise side effects. Supervision ensures dose accuracy and prevents overdosing, which can lead to serious side effects or even death
• Management of side effects: The side effects of weight loss injections tend to be mild but can be severe in some cases. Without proper medical supervision, you might not recognise the warning signs of pancreatitis, kidney problems or other health complications
• Genuine products: Unregulated providers may sell counterfeit or contaminated drugs. There’s no guarantee you’ll get the right dosage or any active ingredient at all. This could put your health at risk with no actual benefits
• Sustainable weight loss: To achieve the best weight loss results, you need to take your medication alongside diet and exercise. A trained and experienced healthcare professional can give you the information and tools you need for long-term change

Order prescription weight loss injections online

Established in 2004, The Online Clinic is one of the UK’s most trusted and experienced online healthcare providers.

Our team comprises UK-licensed doctors, and our service is regulated by the Care Quality Commission (CQC) to ensure a superior patient experience.

In our latest report, the CQC awarded us an overall rating of Good in all five assessed areas – one of the highest possible outcomes.

As an independent online clinic, we have the capacity to handle consultations thoroughly yet quickly.

Your prescription request will be reviewed in just 30-60 minutes during normal working hours (07:00 am-10:00 pm).

Any prescriptions ordered before 3:30 pm Monday-Friday (public holidays excluded) arrive the following business day..

All orders arrive in discreet packaging with no mention of the contents or The Online Clinic for total confidentiality.

Excellent service Excellent service. I filled out my health questionnaire and was advised it was being reviewed. A couple of extra questions and my prescription was granted. I felt confident that I was correctly prescribed. I’ve since been asked to provide blood pressure readings and current weight. I can contact them any time for advice. Very happy with my choice of provider. Nicola

Register online to request a prescription

Become a patient of The Online Clinic and complete your medical health questionnaire today to start your weight loss journey with safe prescription medication.

Useful resources for weight loss injections

NHS

• Weight loss guidelines
• Obesity treatment
• Eating a balanced diet
• Exercise

Cleveland Clinic

• Liraglutide (Saxenda): Uses and side effects
• Semaglutide injection (weight management)
• Tirzepatide injection

Novo Nordisk

• How Saxenda works
• What is Ozempic?
• How Wegovy works for weight loss

Eli Lilly and Company

• How Mounjaro works