Are weight loss injections safe?

Weight loss injections have been a breakthrough for many people who are struggling to lose weight through diet and exercise alone. The injections, which can only be prescribed by healthcare professionals, work by mimicking digestive hormones like glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) to suppress your appetite.

Currently, in the UK, there are 3 main injections available: Mounjaro, Wegovy, and Nevolat, which the Medicines and Healthcare products Regulatory Agency (MHRA) and the National Institute for Health and Care Excellence (NICE) have approved. The active ingredients in all 3 have gone through multiple clinical trials to test their efficacy and safety for weight management. However, it’s normal to have concerns, especially when there’s increased public attention on the potential risks and side effects of these treatments.

Here, we discuss the safety of weight loss injections, what side effects you might experience, how to manage them, and when to seek medical advice.

Weight loss injections, such as Mounjaro and Wegovy, are a type of treatment designed to help people manage their weight more effectively. They contain active ingredients, such as GLP-1 analogues, that mimic hormones your body naturally produces. These hormones help control appetite, slow digestion, and regulate how your body processes food.

By making you feel full sooner and reducing hunger, weight loss injections make it easier to eat less and stick to healthier habits.

➤ Learn more about GLP-1 injections

Weight loss medications might not be right for everyone, that is why it’s important to speak to a doctor or medical prescriber before starting weight loss injections. A doctor will review your medical history, including any conditions, medications, or allergies, to ensure the treatment is safe for you. Being open about your health helps your doctor recommend the best option and reduce potential risks. Rising obesity statistics in the UK highlight why treatments like these are increasingly in demand, but they must always be used responsibly. Never start these injections without professional advice.

When prescribed by a doctor and used correctly, weight loss injections are generally safe and work well. They have been carefully tested in clinical trials and approved by the Medicines and Healthcare products Regulatory Agency (MHRA) in the UK. This means they meet strict safety standards.

Like all medicines, weight loss injections can cause side effects. Most side effects are mild and go away on their own, but rare, more serious problems can happen. Knowing what to expect can help you feel prepared and confident.

Some people may experience side effects when they start using weight loss injections. These are usually mild and go away as your body adjusts. Common side effects include:

• feeling sick (nausea)
• constipation or diarrhoea
• feeling tired or low on energy

Here are some tips to help manage mild side effects:

• eat smaller meals and avoid rich or greasy foods
• drink plenty of water to stay hydrated
• rest if you feel tired

If the side effects don’t go away or bother you, speak to your prescriber.

For detailed information about side effects, see our dedicated pages on side effects for Mounjaro, Wegovy, and Nevolat (liraglutide) in our health guides:

Serious side effects from weight loss injections are not common, but it’s important to know the warning signs. You should stop treatment and seek medical help if you experience:

• severe stomach pain, especially if it spreads to your back. This could be a sign of pancreatitis.
• yellowing of your skin or eyes (jaundice) or very dark urine. These could be signs of liver problems, gallstones or pancreatitis.
• difficulty breathing or swelling in your face or throat. This could mean you’re having a severe allergic reaction.

If you notice any of these symptoms, go to A&E or call 999 immediately.

Pancreatitis, or inflammation of the pancreas, is one of the uncommon but serious risks linked to some weight loss medications, including Mounjaro. Pancreatitis happens when the pancreas becomes irritated or damaged, which can lead to severe symptoms.

Here are some of the reasons why you may not be able to use weight loss injections:

You are allergic to the active ingredients

If you are allergic to tirzepatide, semaglutide, or liraglutide, or any of the other ingredients listed in the preferred injection, you must not take it. You can find a list of ingredients in the patient information leaflet that comes with your injection.

You are pregnant or breastfeeding

The effects of weight loss injections on unborn children are not yet known, so if you are pregnant, think you might be, or are planning to have a baby, you should not take any weight loss injections.

It’s not known if the active ingredient in weight loss medications can pass into breast milk. So, weight loss injections are also not suitable if you’re breastfeeding.

You do not meet the eligibility for prescribing

Weight loss injections are only intended for people who are:

• obese
• overweight and have weight-related health conditions

Usually, this means having a BMI of 30 or more or at least 27 and at least 1 other weight-related illness, such as high blood pressure, obstructive sleep apnoea, or cardiovascular disease.

If these do not apply to you and you take weight loss injections, this is putting you at risk of severe side effects and potentially serious complications, like pancreatitis or gallbladder issues.

You have certain health conditions

If you have certain health conditions, it’s not recommended that you take weight loss injections because it can make them worse, cause interactions, or lead to severe side effects.

Before taking Mounjaro, Wegovy, or Nevolat, tell your doctor if you have or have ever had any health conditions, but especially:

• severe liver or kidney problems
• pancreatitis
• an allergic reaction to other weight loss medications
• gallbladder issues
• thyroid conditions
• digestive issues
• diabetic eye disease

You are over 75

Nevolat or generic liraglutide is not recommended for people who are over 75, as there is not enough research into how it affects people of this age. Your doctor may recommend Wegovy or Mounjaro as an alternative, depending on your medical history and personal situation.

Weight loss injections like Mounjaro, Wegovy, and Nevolat are intended for people who are living with obesity or those who are overweight with a related health condition. However, some people may try to obtain these medications while being within a healthy weight range or who have an underlying or undiagnosed eating disorder, like anorexia nervosa, bulimia, or atypical disordered eating behaviours.

When to contact 111

Call 111 for advice if you have symptoms that are worrying but not urgent, like:

• nausea or vomiting that won’t go away
• mild stomach pain that lasts for a few days
• diarrhoea that doesn’t stop after two days
• you have not opened your bowels or passed gas for several days, especially if your stomach is also bloated

111 can give you advice and tell you if you need to see a doctor.

When to go to A&E

Go to A&E or call 999 if you have serious symptoms, like:

• severe stomach pain that doesn’t go away.
• trouble breathing, wheezing, or swelling in your face or throat.
• signs of liver or gallbladder problems, like yellowing of your skin or eyes.

How to stay prepared

• Keep your medication details handy in case you need them in an emergency.
• Write down any symptoms you notice and tell your doctor at your next appointment.

At ZAVA, we’re here to support you through every stage of your weight loss journey. From day 1, you’ll have our full support, including:

✓ regular check-ins with your doctor

✓ free weight loss support materials and guides from our in-house nutritionist

✓ dedicated help from our patient care team

With medication delivered right to your door, we make sure your journey is safe, simple, and tailored to you.

How it works

When you request weight loss medication from us, you will need to complete an online consultation, which will ask you about your health and lifestyle. This is so our doctors can make sure the medication is safe and suitable for you to take. It will involve answering questions about your medical history, any medications you are taking, and your current lifestyle.

As part of this consultation, you will need to provide some photos, so that we can verify your BMI. Once your medication is approved, you will also be asked to provide photos at key stages during your treatment, so we can safely monitor your progress and make informed decisions about your care.

When you’re ready to go up to the next dose of your weight loss injection, you will need to complete a repeat questionnaire for our doctors to review and confirm if the dose you have selected is right for you. The process helps to make sure that your weight loss journey is safe and sustainable. For example, if you are struggling with side effects, you may be advised to stick to your current dose for longer to see how your body responds.

If you have questions or concerns at any time while you’re taking weight loss medication, you can contact our team for advice.

➤ Explore the ZAVA weight loss service

Finding reliable information

There is lots of information on the internet about weight loss injections, tips and tricks to help you lose weight quickly, and well-publicised success stories. However, it is important that you use trusted sources when learning about weight loss injections to give you an honest, balanced, and accurate picture.

At ZAVA, our content goes through a series of reviews, including peer and medical reviews, to make sure the information is as accurate as possible at the time it’s published. If you’d like to learn more, visit our dedicated weight loss pages in our further reading section at the bottom of this page.