How Do Weight Loss Injections Work?

Understanding Weight Loss Injections

Some people struggle with obesity and weight loss despite dietary changes and increased physical activity. Several brands of weight loss injections are available in the UK, but how do they work? 

Weight loss injections, also known as weight loss shots or anti-obesity injections, help reduce or control excess body fat. 

In this article, we’ll explore the different types of weight loss injections, how they work, and their effectiveness.

Types of Weight Loss Injections Available

1. Mounjaro: Mounjaro is a pre-filled, once-weekly injection pen designed to support weight loss. It has a dual action, working in two ways to help your body regulate metabolism. 

It mimics the effects of two natural hormones, GIP and GLP-1, to help your body balance blood sugar levels and appetite, leading to significant weight loss.

Mounjaro

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• Approved Weight Loss Treatment
• Suitable for adults with a BMI of +30kg/m²
• Pre-filled injection pen

• Discreet delivery next working day
• Online prescription - No doctor visit

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2. Wegovy: Wegovy is a medication that helps with weight loss. It's given by injection once a week and contains a substance called semaglutide. 

Semaglutide works by copying the effects of a natural hormone in our body called GLP-1. GLP-1 is released after eating and helps control appetite and blood sugar levels. By mimicking GLP-1, semaglutide helps us lose weight gradually

Wegovy

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• Approved Weight Loss treatment
• Weekly injection
• Reduces risk of heart attack & stroke

• Discreet delivery next working day
• Online prescription - No doctor visit

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How Do Weight Loss Medications Work?

Weight loss medications, such as Wegovy, Mounjaro, and Mysimba, contain substances or hormones that promote weight loss. These substances help control appetite, regulate blood sugar levels, and break down fat.

This is how they work:

Appetite Suppression

These medications target the brain's appetite centres, making you feel fuller, faster and longer. They also slow down the rate at which your stomach empties, keeping you feeling fuller for longer. This means you'll feel less hungry and eat fewer calories, which can lead to weight loss.

Enhance Insulin Secretion and Sensitivity

These weight-loss injections help your body better use insulin, a hormone that controls blood sugar levels. 

Insulin allows sugar from digested food to enter your cells, where it's used for energy. By improving insulin sensitivity, these injections help maintain stable blood sugar levels and prevent spikes that can contribute to weight gain. This process supports weight loss and overall health.

Decrease Glucagon Release

Glucagon is another hormone produced by the pancreas, but it has the opposite effect of insulin. 

When blood sugar levels drop too low, glucagon helps raise them to a normal level. Weight loss pens lower glucagon levels, which helps keep blood sugar levels stable and in control.

How Effective are Weight Loss Injections?

Weight loss injections have been shown to be effective in aiding weight loss. However, results may vary depending on the specific medication and individual factors, such as body chemistry, starting weight, diet, exercise, weight, and overall health.

According to the National Institute of Diabetes and Digestive and Kidney Diseases, adults who combine prescription medications with a lifestyle program typically achieve a 3-12% greater weight loss compared to those relying solely on lifestyle changes, resulting in a significant additional reduction in body weight over the course of one year.

Clinical trials by Wegovy showed participants achieved an average of 15% mean weight loss, approximately 35lbs, over two years. Mounjaro has shown significant weight loss results, with some studies reporting an average weight loss of up to 20% of body weight over 72 weeks. Meanwhile, Saxenda users achieved an average weight loss of 9.2%, or 21 pounds, over 56 weeks.

To achieve the best results from weight loss injections, combine them with healthy habits, such as eating a lower-calorie diet and exercising more. Beyond weight loss, these medications can also improve metabolic health by regulating blood sugar levels, reducing blood pressure, and enhancing cholesterol levels.

Who Should Consider Weight Loss Injections?

Weight loss injections may be suitable for individuals who:

• Have a body mass index (BMI) of 30 or higher.
• Have a BMI of 27 or higher with at least one weight-related condition, such as hypertension, type 2 diabetes, or high cholesterol.
• Are having difficulty losing weight through diet and exercise alone.
• Want a non-surgical and medically supervised weight loss programme.
• Are willing to make lifestyle changes to maintain weight loss.

Potential Side Effects

Like all medications, weight loss injections can have side effects. Some may be mild and temporary, while others can be serious and life-threatening. 

Common side effects include nausea, vomiting, diarrhoea, and constipation, which usually go away as your body gets used to the treatment. 

Although rare, there are potential risks like pancreatitis, heart rate changes, thyroid tumours, gallbladder disease, and kidney damage, which require immediate medical attention.

Finding the Right Provider

When searching for a provider, it's essential to verify their reputation and read patient reviews. You can check the reviews of Prescription Doctor on Trustpilot. 

Make sure your provider is qualified and experienced. Research their credentials, read reviews from trusted sources, and consult a healthcare professional to ensure safe and effective treatment. 

While reviews can be helpful, a healthcare professional will assess your individual needs and guide you through the process.

Conclusion

Weight loss injections can be a helpful tool for people trying to manage their weight. However, it's essential to remember that they work best when combined with a healthy diet and regular exercise. 

It's also important to be realistic about the results and to focus on making long-term lifestyle changes rather than relying solely on medication to lose weight.

Authored & Reviewed By

Mohamed Imran Lakhi

MPharm - Lead Pharmacist

Imran Lakhi is the superintendent pharmacist and founder at Prescription Doctor. He has been at the core of our team.

Published on: 19/05/2023 Reviewed on: 05/06/2025