Your guide to weight loss injections in the UK 

Reviewed by Dr Harvinder Chahal, Consultant Endocrinologist

Table of contents

• About weight loss injections
• Weight loss injections available in the UK
• Using weight loss injections
• How to get weight loss injections

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In recent years, weight loss injections have emerged as one of the most talked-about and transformative tools for managing obesity and supporting weight loss. Once reserved for the treatment of diabetes, weight loss injections are now at the forefront of medical weight management, offering an alternative solution for those who have previously struggled with traditional diet and exercise plans.

However, while weight loss injections such as Wegovy and Mounjaro are in high demand, it’s important to understand that weight loss injections aren’t a miracle cure – and should always be used in conjunction with diet and lifestyle changes. In this blog, we’ll explore how weight loss injections work, break down what options are available in the UK, and help you decide whether weight loss injections are right for you.

All treatment options mentioned are available at our private weight loss clinic in Marylebone, London.

About weight loss injections

How do weight loss injections work?

The weight loss injections that are gaining popularity in the UK are GLP-1 receptor agonists (occasionally shortened to GLP-1 RA). They’re more commonly known by their brand names, which are Mounjaro, Wegovy, and Saxenda.

All three of these drugs contain a different active ingredient – tirzepatide for Mounjaro, semaglutide for Wegovy, and liraglutide for Saxenda – but they work in the same way.

GLP-1 receptor agonists regulate blood sugar levels, which is why they are used by patients with type 2 diabetes. They do this by mimicking a naturally occurring hormone GLP-1, which is released when you consume food.

GLP-1 agonists trigger the body to produce more insulin, which lowers blood sugar levels. However, they also cause food to pass more slowly from your stomach to your small intestine, which leaves you feeling fuller faster and for a longer period of time. Subsequently, many patients find themselves eating less and lose weight.

Mounjaro is slightly different as it mimics both GLP-1 and another hormone called GIP, which also regulates blood sugar levels and metabolism.

When were weight loss injections approved in the UK?

GLP-1 agonists were originally developed and used as a treatment for type 2 diabetes. In the UK, the first GLP-1 agonist was licenced for the treatment of type 2 diabetes in 2007.

Because GLP-1 agonists have weight loss as a secondary effect, they were also found to be helpful for non-diabetic patients struggling with obesity. In the UK, the first GLP-1 agonist to be approved for weight loss was liraglutide (Saxenda) in 2017, semaglutide (Wegovy) in 2023, followed by tirzepatide (Mounjaro) in 2024. At present, these are the only three GLP-1 agonists approved in the UK for weight loss purposes.

Ozempic, which also contains semaglutide as an active ingredient, is only approved for the treatment of type 2 diabetes in the UK.

What is the best injection for weight loss?

There is no ‘best’ weight loss injection – it’s entirely subjective depending on your body and circumstances. Your consultant will be able to advise on the different options available, as well as which injection they think would suit your case best.

Research has determined that Mounjaro may be slightly more effective for weight loss thanks to its dual-action approach in mimicking both GLP-1 and GIP hormones. However, if Mounjaro isn’t an option for you, Wegovy and Saxenda are also valuable treatment solutions for supporting effective weight loss.

Are weight loss injections safe?

When prescribed and monitored by a healthcare professional, weight loss injections are generally considered to be safe and effective. Additionally, before their secondary application as a weight loss aid, these injections were (and have continued to be) successfully used in patients with type 2 diabetes. However, like any medication, weight loss injections come with potential side effects – some of which can be severe in rare instances.

Weight loss injections become dangerous if they have been inappropriately prescribed (e.g. to someone who does not meet the criteria) and/or purchased from unauthorised sources.

What are the side effects of weight loss injections?

Side effects of weight loss injections may include nausea, constipation, diarrhoea, vomiting, heartburn, stomach pain, headache, tiredness (fatigue), or dizziness. These should typically go away with time but contact your consultant if you have any ongoing concerns.

Some people will experience a reaction at the site of their injection, which may include redness, bruising, itching, and swelling. This can typically be treated with an antihistamine.

Severe side effects of weight loss injections include pancreatitis and gallbladder problems.

If you are experiencing severe or intolerable side effects, please get in touch with your consultant as soon as possible. If you have severe abdominal pain or are having an allergic reaction following injection, please attend your nearest A&E department.

Who can take weight loss injections?

You will typically qualify for weight loss injections if:

• you have a BMI over 30 or
• you have a BMI of over 27 with a weight-related condition that would improve with weight loss (e.g. high blood pressure, high cholesterol, heart disease, sleep apnoea, fatty liver, polycystic ovary syndrome, or musculoskeletal disorders)

Additionally, you should also consider whether you are able to commit to long-term diet and lifestyle changes. This includes following a balanced diet for weight loss and increasing physical activity.

What are the alternatives to weight loss injections?

Weight loss injections may not be suitable for everyone, and they aren’t the only options available. For patients who would prefer a non-injectable option, oral medications such as orlistat (branded as Alli or Xenical) can help reduce fat absorption from food.

We can also refer you on to Cromwell Hospital, where you can access further surgical and non-surgical options. These include non-invasive swallowable gastric balloons (Orbera and Allurion) and endoscopic sleeve gastroplasty (ESG), as well as traditional weight loss surgery such as gastric band, gastric bypass, and sleeve gastrectomy – all delivered by world-leading bariatric consultants.

Weight loss injections available in the UK

Mounjaro injection

Mounjaro is the brand name for a drug called tirzepatide.

Unlike other weight loss injections, Mounjaro also mimics a hormone called glucose-dependent insulinotropic polypeptide (GIP). Like GLP-1, GIP also stimulates the release of insulin. This dual-action approach may facilitate more effective weight loss than other types of injections, with patients in a clinical trial losing on average 20.9% of their bodyweight.

Wegovy injection

Wegovy is the brand name for a drug called semaglutide, which is also the same active ingredient in Ozempic. Patients in a clinical trial lost on average 14.9% of their bodyweight.

Is Wegovy the same as Ozempic?

Wegovy and Ozempic contain the same active ingredient (semaglutide). In the UK, Wegovy is approved for weight loss while Ozempic is only approved for the treatment of type 2 diabetes.

The main difference is in the dosage. Wegovy (for weight loss) requires a higher dosage than Ozempic (for diabetes management).

Saxenda injection

Saxenda is the brand name for a drug called liraglutide, which helps regulate blood sugar levels. Patients in a clinical trial lost on average 8% of their bodyweight.

Using weight loss injections

How do you take weight loss injections?

Weight loss injections are typically administered once a week (Wegovy and Mounjaro) or once daily (Saxenda) using a pre-filled pen that you inject under the skin, usually in the stomach, thigh, or upper arm. The pens are designed to be easy to administer at home, but your consultant will ensure you feel comfortable and confident in using them before your treatment begins.

Most weight loss injections start a low dose, which helps your body adjust to the medication and minimises the risk of side effects; the dose is then gradually increased over several weeks. You will be advised to rotate your injection sites to avoid skin irritation, and you should also ensure that you aren’t reusing needles.

What should I eat while using weight loss injections?

Weight loss injections should always be accompanied by a diet and exercise plan for optimal results. At London Medical, your consultant will design a treatment plan based on your lifestyle and preferences. Typically, this will mean eating in a calorie deficit and adhering to a balanced diet that prioritises whole foods, like fruits and vegetables, lean protein, and healthy fats. You will be advised to reduce your intake of processed and high-sugar foods, which may worsen side effects such as nausea and digestive discomfort.

Weight loss injection plateaus

Most people who are in the process of losing weight, whether using injections or not, will experience a plateau. In the beginning stages of weight loss, you will lose a significant amount of weight simply through a calorie deficit and medication (if being used). However, your body will eventually adjust to accommodate these changes, which means that weight loss slows down and often stalls completely.

While weight loss plateaus can be frustrating, they can often be resolved by reviewing and adjusting your treatment plan. You may need to amend your calorie intake, increase physical activity, or discuss alternative strategies with your consultant.

How to get weight loss injections

Can I buy weight loss injections online?

The ease of purchasing weight loss injections online can be tempting for many patients looking to lose weight quickly. However, when improperly prescribed or used, weight loss injections can be very dangerous.

Additionally, there have been anecdotal reports of people ending up seriously ill after unknowingly purchasing counterfeit drugs online, through social media, or other unauthorised channels – which is why they should only ever be prescribed by and used under the supervision of a medical professional.

At London Medical, we will only prescribe weight loss injections following a detailed medical consultation. This is so we can talk to you and find out more about your weight loss goals, take an in-depth medical history, and thoroughly assess your suitability for treatment. We will also talk you through possible side effects and how to manage them.

If you’re interested in weight loss but unsure about injections, we can also advise on alternative treatment options.

Weight loss injections at London Medical

At London Medical, we provide Wegovy, Mounjaro, and Saxenda, as well as alternative treatments like orlistat.

During your first consultation, your consultant will explore your current health, medical history, and your motivations for losing weight. Whether you opt for weight loss injections or an alternative treatment, your consultant will devise a personalised treatment plan to help you achieve best results. You will also have regular follow-up appointments to monitor your progress and manage any side effects.

To enquire about weight loss solutions, including injections, please get in touch with our Appointments team on 0800 0483 330.