How Do Weight Loss Injections Work?
Table of contents:
- What is a Weight Loss Injection?
- How Do Weight Loss Injections Work?
- Are Weight Loss Injections Safe?
- How to Qualify for Weight Loss Injections
- What are the Different Types of Weight Loss Injections?
- Potential Side Effects from Weight Loss Injections
- Do Weight Loss Injections Work?
- Weight Loss Injections Before and After
- How to Get Weight Loss Injections
- Trusted Weight Loss Support from Prescription Doctor
Weight loss injections are rapidly gaining popularity in the UK as more people become aware of their potential benefits. Demand for Wegovy, Mounjaro, and Nevolat has skyrocketed due to their reputation for promoting rapid weight loss, and research suggests that their effects are far superior to those of diet and exercise alone.
People often lose a substantial amount of weight on these medications, with some studies reporting weight reductions of up to 25% over a year of treatment. The results are staggering, and have many people asking: ’How do weight loss injections work?’
Weight loss injections, or GLP-1 agonists, are a group of medications that promote weight loss by suppressing food cravings and appetite. But what other effects do these drugs have? Are they safe, and who is eligible for them? We’ll discuss the answers to these questions, and more, so you can make an informed decision about how to proceed with your weight loss journey.
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What is a Weight Loss Injection?
Weight loss injections are injectable medications that promote weight loss by suppressing appetite. They mimic the effects of naturally produced hormones that signal to your brain when you are full, thereby reducing ‘food noise’ and cravings.
In one study, participants receiving weight loss injections reduced their calorie intake by up to 39% compared to those on placebo treatment. This sharp reduction in calorie intake often leads to dramatic weight loss and makes it easier for people to stick to a diet and exercise plan.
Different types of weight loss injections contain different active ingredients. The main options licensed for prescription in the UK are:
- Wegovy (Semaglutide)
- Nevolat (Liraglutide)
- Mounjaro (Tirzepatide)
How Do Weight Loss Injections Work?
Wegovy (semaglutide) and Nevolat (liraglutide) contain drugs called glucagon-like peptide-1 (GLP-1) agonists, which mimic the effects of a hormone called GLP-1. GLP-1 is released from the small intestine in response to food intake and promotes satiety, or a feeling of ‘fullness.’
Mounjaro (tirzepatide) is a dual agonist that mimics two hormones: GLP-1 and GIP (gastric inhibitory polypeptide). Like GLP-1, GIP is thought to reduce appetite and food intake. By simulating the effects of both hormones, tirzepatide may promote greater weight loss than drugs that only mimic GLP-1.
However, reduced hunger is only one of the potential health benefits of weight loss injections. These medications can also enhance insulin production and sensitivity, as well as inhibit the release of glucagon, to help control blood sugar levels.
Here's an explanation of how weight loss injections work in more detail:
Appetite Suppression
GLP-1 agonists primarily promote weight loss by suppressing appetite. They slow the rate at which food moves through the stomach, making users feel full more quickly than usual. They may also reduce food cravings by dampening the anticipation of food and making high-fat foods less appealing.
These combined effects mean people on weight loss injections typically eat far less than usual, and may avoid energy-dense foods that contain a lot of fat. This makes it much easier for users to stick to a calorie-restricted diet and often leads to rapid weight loss.
Enhanced Insulin Secretion and Sensitivity
GLP-1 and GIP agonists were originally developed to treat type 2 diabetes by helping the body regulate its blood sugar levels. They stimulate insulin secretion during food intake, which promotes the uptake of glucose by the cells and helps keep blood glucose levels stable. These medications also improve insulin sensitivity, meaning the body’s cells are more responsive to insulin and better at absorbing glucose from the blood.
Reduction in Glucagon Release
Glucagon is a hormone produced by the pancreas. It stops blood sugar levels from dropping too low by preventing uptake of glucose by the liver, so more stays in the bloodstream. It also triggers the liver to convert stored glucose (called glycogen) into a usable form, which is released into the bloodstream.
People with type 2 diabetes may have relatively elevated glucagon levels, which can contribute to high blood sugar. GLP-1 agonists help counteract this by inhibiting the release of glucagon, thereby contributing to better glycemic control.
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Are Weight Loss Injections Safe?
Weight loss injections are generally considered safe, and may lower your risk of weight-related health problems like heart attack and stroke. However, like all medications, they have the potential to cause side effects.
Most people on weight loss injections won’t experience anything more serious than temporary gastrointestinal symptoms. In rare cases, weight loss injections can trigger more serious health conditions like pancreatitis and gallbladder disorders. For the sake of safety, it is recommended that you take weight loss medications only under the guidance of a licensed clinician.
How to Qualify for Weight Loss Injections
Weight loss injections are prescribed to people who are obese (with a BMI over 30 kg/m2) or overweight (with a BMI over 27 kg/m2) with at least one weight-related health problem. Weight-related medical conditions that may qualify someone for weight loss injections include:
- High blood sugar levels (i.e., prediabetes or type 2 diabetes)
- High blood pressure
- Elevated blood lipid levels
- Obstructive sleep apnoea
- Heart disease
What are the Different Types of Weight Loss Injections?
There are three main weight loss drugs available for prescription in the UK: tirzepatide, semaglutide, and liraglutide. These medications are sold under different names, with the most popular options including Mounjaro, Wegovy, and Nevolat.
Mounjaro
The active ingredient in Mounjaro is tirzepatide, which is a dual GLP-1 and GIP agonist. This means it mimics the effects of two hormones, unlike semaglutide and liraglutide (which are GLP-1 agonists). Some studies suggest that the dual action of tirzepatide makes it a more effective weight loss tool than GLP-1 agonists like semaglutide and liraglutide.
Mounjaro is administered once a week, with dose increases every four weeks. The starting dose of Mounjaro is 2.5 mg, and the highest possible maintenance dose is 15 mg per week.
Mounjaro
- Approved Weight Loss Treatment
- Suitable for adults with a BMI of +30kg/m²
- Pre-filled injection pen
Wegovy
Wegovy is a weekly weight loss injection that contains semaglutide as its active ingredient. Semaglutide is a GLP-1 agonist and promotes weight loss by mimicking the appetite-suppressing effects of the GLP-1 hormone. This can help people achieve significant weight loss, with one study reporting weight reductions of up to 17.4% over 68 weeks of treatment.
Wegovy
- Approved Weight Loss treatment
- Weekly injection
- Reduces risk of heart attack & stroke
Nevolat
Nevolat is the generic version of Saxenda, containing liraglutide, a type of GLP-1 agonist. Like semaglutide and tirzepatide, liraglutide helps people lose weight by suppressing appetite and calorie intake.
The main difference between Nevolat and the other weight loss injections discussed here is the frequency of dosing. Whereas Mounjaro and Wegovy are injected once a week with dose increases every four weeks, Nevolat is formulated for daily use with weekly dose increases.
Nevolat
- Approved Weight Loss treatment
- Once-daily injection
- More affordable than branded treatments
Potential Side Effects from Weight Loss Injections
Like all medications, weight loss injections have the potential to cause side effects. The side effects of Mounjaro, Wegovy, and Nevolat vary slightly, but the most common across all three are gastrointestinal symptoms. Digestive issues may affect over 10% of people on weight loss medications, and include:
- Diarrhoea
- Constipation
- Nausea
- Vomiting
- Indigestion
- Abdominal pain
Most of the time, the gastrointestinal side effects of weight loss injections are mild to moderate and get better within a few days. However, persistent diarrhoea or vomiting can lead to severe dehydration and other health complications, like kidney damage.
Rarely, weight loss injections can cause serious health problems such as pancreatitis, gallbladder disorders, and kidney failure. If you have any concerns about severe or persistent side effects, contact a licensed clinician for advice.
Do Weight Loss Injections Work?
Clinical studies have consistently demonstrated the efficacy of tirzepatide, semaglutide, and liraglutide in lowering blood sugar levels and promoting weight loss.
Tirzepatide, the active ingredient in Mounjaro, may be the most effective of the three for weight reduction. One study reported that tirzepatide outperformed semaglutide and liraglutide in terms of weight loss and led to an average body weight reduction of 18%, compared to 12% for semaglutide and 5% for liraglutide. Therefore, Mounjaro may be the preferred option for people hoping to lose a significant amount of weight.
However, all of the weight loss injections currently available in the UK have seen success in clinical trials.
People using semaglutide (Wegovy) may lose up to 15% of their total body weight within a year of treatment. Research into the efficacy of liraglutide suggests that people can lose 5 - 8% of their body weight on this medication, with one study reporting a 5.8% reduction in one year of treatment.
These medications are comparable in terms of safety, with the most common side effects across all three being temporary gastrointestinal problems. Therefore, the main things to consider when choosing a medication are price and the frequency of dosage.
Weight Loss Injections Before and After
Clinical research results suggest that weight loss injections are a safe and highly effective way to shed weight. However, medicine is a deeply personal choice, and starting a new treatment plan requires careful consideration and thorough research. When making your decision, it can be helpful to hear about the real-life experiences of people who have used these medications.
Many people on Mounjaro see a significant improvement in their weight loss progress, with reduced food cravings making it much easier to stick to a calorie-reduced diet. Users report positive health changes such as improved blood pressure, cholesterol levels, and insulin sensitivity following Mounjaro treatment. The weight loss results are also extraordinary, with one user shedding over 200 lbs (92 kg) in under two years of treatment.
Wegovy has been found to produce similar results, illustrated by impressive before-and-after photos. People on Wegovy share that they experience a boost in their quality of life and feel fitter, stronger, and more confident after weight loss.
How to Get Weight Loss Injections
If you would like to try Mounjaro, Wegovy, or Nevolat, there are a few routes you can take to access these medications. People eligible for these treatments (i.e., those with obesity or who are overweight with at least one weight-related health problem) may be able to get them on the NHS.
However, the quickest and most convenient way to get weight loss injections is often with the help of an online pharmacy like Prescription Doctor. Online pharmacies have a lower qualifying threshold than the NHS, and you can quickly and easily confirm your eligibility for treatment via online questionnaires. These companies can also ship your medication directly to your address, eliminating the need for in-person appointments and purchases.
Trusted Weight Loss Support from Prescription Doctor
If you’re thinking about using weight loss injections as part of your health journey, Prescription Doctor is here to help. We’re dedicated to helping people just like you achieve their goals, providing specialist support every step of the way.
We offer a range of licensed weight loss treatments, including injections and tablets, while our licensed clinicians will assess your unique circumstances to recommend what they believe is the best option for you. They will also regularly check in with you to monitor progress and ensure everything is working as it should.
As well as answering questions such as “How do weight loss injections work?”, we provide a comprehensive library of resource articles on various subjects, including diet plans (vegan and non-vegan), and how to notice when you’re losing weight. All of this comes as standard with our service.
Want your medication delivered quickly and discreetly? No problem. We dispatch all products in plain packaging, while orders approved before 3pm on a weekday are eligible for next-day delivery. We provide a straightforward and hassle-free service that you can rely on.
Ready to get started? Sign up for your weight loss consultation today.
Authored By
Kate Latham
Medical Content WriterPublished on: 19/05/2023 Re-Published on: 12/09/2025
Reviewed By
Mohamed Imran Lakhi
MPharm - Lead PharmacistReviewed on: 12/09/2025
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