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What are weight loss injections?

Weight loss injections are a type of prescription medication for weight loss that can be more effective than weight loss pills or low-calorie diets. Weight loss pills and weight loss injections are both licensed for people with a BMI of 30 or more (or less than this if you also have certain health conditions). The NHS will usually only fund injection weight loss treatment if your BMI is 35 or more.

Medically reviewed by

Daniel Atkinson, GP Clinical Lead

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Medically reviewed by

Dr Daniel Atkinson

GP Clinical Lead

on July 11, 2024.

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The weight loss injections available are Saxenda, Wegovy, and Mounjaro. Talk to us if you’re thinking of trying weight loss injections and one of our clinicians will explain how each of them works and answer any questions that you might have.

How do weight loss injections work?

Although the active ingredients in weight loss injections (WLI) have different names, they’re mostly from the same family of drugs and work in a similar way.

Wegovy contains the active ingredient semaglutide, a component almost identical to the hormone known as GLP-1, which is secreted by your gut when you eat something.

Semaglutide works by manipulating your appetite for you to feel full quicker, but also by slowing down the emptying of the stomach, so you can feel full for longer after you eat. It’s often prescribed as a treatment for type-2 diabetes under the name Ozempic, so if you’re at high risk, or you already have the condition, it might be the ideal option for you.

Wegovy also targets the parts of the brain responsible for appetite control. This means that you’ll likely reduce the amount of calories you eat and go on to lose weight. Both Ozempic and Wegovy should be taken alongside a calorie controlled diet and an increase in exercise.

Saxenda uses the active ingredient liraglutide, a synthetic derivative of the hormone GLP-1. This hormone is responsible for your appetite, so by topping up with liraglutide your body will think it’s full faster, and for longer.

Zepbound and Mounjaro contain the active ingredient tirzepatide, which is a GLP-1 receptor and a GIP receptor agonist. It works in a similar way to Wegovy, by suppressing your appetite and signals your brain to make you feel full and satiated. This prevents overeating. Zepbound and Mounjaro appear to reduce more of the visceral fat around abdominal organs than some of the other weight loss injections and preserve more muscle mass.

All four weight loss injections listed here stabilise blood sugar through insulin production. This can make you feel less cravings, giving you better control over what and how much you eat.

Do they actually help you lose weight?

Yes, these injection drugs can cause significant and sustained weight loss when used correctly. Usually combined with a reduced calorie diet and an increase in physical activity.

There’s clinical evidence that liraglutide, the active ingredient in Saxenda, helps you lose significant weight sustainably, with the added, unique benefit of improving your glycemic levels.

Wegovy clinical trials found statistically significant weight loss results for participants when compared with a placebo group. The weight loss results were observed in participants irrespective of their age, gender, race, ethnicity and initial BMI.

Likewise, in a clinical study, people using Zepbound lost up to 20% of body weight over 72 weeks.

But it’s important to continue to practise the healthier habits mentioned above – eating healthily and exercising regularly – after finishing treatment to make sure that you don’t regain the weight you’ve lost during treatment.

Are Wegovy and Ozempic better than Saxenda?

Both semaglutide and liraglutide, the active substances in Ozempic, Wegovy and Saxenda, mimic the hormone GLP-1. These active ingredients are very similar to the naturally occurring GLP-1 hormone.

Saxenda has been approved as a weight loss medication, and Ozempic is technically a type-2 diabetes medication. But clinicians saw significant weight loss in diabetes patients using this medication. Initially, some clinicians prescribed Ozempic as an off-label weight loss injection. But since then, semaglutide has been licensed for use in weight loss under a new brand name: Wegovy.

A study that compared the effectiveness of semaglutide, with liraglutide and placebo, found that injecting semaglutide can result in significant weight loss with minimal side effects, and about 37-65% of people who take it will see a decrease of 10% of their excess weight in up to 52 weeks after the treatment starts. In the same time frame, only 25.2% of people taking the highest dose of liraglutide (3mg) achieved the same 10% loss of excess body weight.

It’s important to take into account that the study on the efficacy of semaglutide was done on people without type 2 diabetes, whilst everyone on the study on the efficacy of liraglutide was diagnosed with type 2 diabetes before the study.

What’s the difference between Saxenda and Wegovy?

Saxenda and Wegovy are similar weight loss medications. Saxenda uses the active ingredient liraglutide, whereas Wegovy uses semaglutide. Both active ingredients fall into the same category of medication known as GLP-1. Wegovy and Ozempic are different brand names for the same active ingredient, the doses are slightly different as one is used to treat type 2 diabetes and one is for weight loss.

A course of Saxenda requires a daily injection and the dosage is usually adjusted over time, until you reach the usual recommended dosage of 3.0mg. Alternatively a course of Wegovy just uses a weekly injection and the dosage usually starts at 0.25mg and increases to 2.4mg over a few months.

Wegovy has been shown to be a more effective weight loss medication than Saxenda. This is due to the potency of the active ingredient. Patients using Wegovy may prefer the treatment over Saxenda because it requires a weekly injection instead of a daily injection, so it’s less effort, and less invasive.

How are Zepbound and Mounjaro different from other weight loss treatments?

Zepbound and Mounjaro both contain the active ingredient tirzepatide, which differs from the active ingredients in Wegovy (semaglutide) and Saxenda (liraglutide). While tirzepatide, semaglutide, and liraglutide all act as GLP-1 receptor agonists, tirzepatide also acts as a GIP receptor agonist. Although GIP receptors work similarly to GLP-1 receptors, this dual action makes tirzepatide more effective for weight loss. This is proven in studies that show individuals using tirzepatide had greater weight loss than those using semaglutide.

Are weight loss injections safe?

Yes, when used correctly weight loss injections are safe. However, all weight loss treatments can cause side effects.

Ozempic is prescribed for diabetes. It is safe to use for weight loss but is an off-label treatment when prescribed for this purpose.

Wegovy is a prescription treatment specifically for weight loss and has undergone rigorous clinical trials. But it’s common for people who use it to experience nausea, particularly when starting the medication or increasing the dose. Similar to Wegovy, the most common side effects reported for Zepbound and Mounjaro were nausea. There are ways you can limit the effects of nausea when using the injections, by drinking plenty of water and avoiding more stodgy, fattier foods. ,

The side effects of stopping weight loss injections tend to be minimal. Since they’re not addictive medications, it’s not likely they’ll cause withdrawal.

Some people may find that they put weight on again after finishing treatment, because they’re no longer feeling the appetite-suppressing properties of the drug. For this reason, it’s important to adopt and adhere to healthy eating and regular exercise while you’re taking treatment, and continue these habits after completing treatment. This will help you to maintain the weight loss you’ve achieved and lower your risk of regaining weight.

This page was medically reviewed by Dr Daniel Atkinson, GP Clinical Lead on July 11, 2024. Next review due on July 11, 2026.

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Disclaimer: The information provided on this page is not a substitute for professional medical advice, diagnosis, or treatment. If you have any questions or concerns about your health, please talk to a doctor.