What Are GLP-1 Injections and Are They Safe?

How GLP-1 agonists work

GLP-1 medications work by mimicking natural hormones that are produced during the digestive process. Medications like Wegovy and Saxenda are known as GLP-1 agonists because they mimic the hormone GLP-1 only. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates both the GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. 

The GLP-1 hormone helps your body by binding to specific receptors in the pancreas, brain and the digestive system. This stimulates the pancreas to release insulin in response to elevated blood sugar levels and helps to lower glucose in the bloodstream. The GLP-1 hormone also slows down gastric emptying (the rate at which food leaves the stomach), which makes you feel fuller for longer and reduces the appetite signals to the brain.

The GIP hormone is the second hormone targeted by dual agonists and also plays a role in regulating blood sugar. By enhancing insulin release and may offer additional benefits in managing metabolism and fat storage.

By combining these two hormones, the dual GLP-1 agonists increase the medication’s effectiveness. Together, they work to better regulate blood sugar levels, suppress the appetite, slow down digestion and promote weight loss while supporting improved metabolic health.

Clinical impact studies

Large clinical trials have evaluated GLP-1 and dual GIP/GLP-1 medicines for people who meet specific criteria. In these studies, many participants achieved at least 5% weight loss, and average weight reductions varied between medicines, doses and trial populations. Results from individual trials for medicines such as tirzepatide, semaglutide and liraglutide are summarised in their patient leaflets and prescribing information.

These results support the growing use of GLP-1 medications in clinical weight management, especially when lifestyle changes alone have not been effective. To have the best results, it's advised to combine the GLP-1 injections with a diet and lifestyle change.

Who is eligible for GLP-1 medication?

GLP-1 medications are typically prescribed for adults who meet certain criteria related to weight and overall risk factors. You may be eligible for a GLP-1 injection if you have:

• A BMI of 30 or higher or

• A BMI of 27 or higher with other weight-related health conditions, such as high blood pressure, prediabetes or type 2 diabetes, high cholesterol or cardiovascular issues

These medications are usually considered after lifestyle interventions like diet and exercise have not been effective on their own.

It's important to have a consultation with a clinician before starting treatment. They will review your medical history, any medications you take and will  assess whether any of the GLP-1 injections is an appropriate and safe treatment for you.

Are GLP-1 injections safe?

When prescribed and used correctly under medical supervision, GLP-1 injections are generally considered safe and effective for weight management. These medications have undergone rigorous clinical testing and are approved for use in the UK and many other countries.

The safety of the medication depends on several factors, having a consultation to ensure you're a suitable candidate, having the correct dosages with a dosage schedule and that your progress is being monitored by a clinician. This gives you professional guidance and support should you need it, such as managing side effects or issues with the pens.

Important safety warnings

As the popularity of GLP-1 medications has increased, so has the illegal and falsified versions of medications, such as semaglutide, liraglutide and tirzepatide. They are being sold online and promoted on social media. These products are often marketed through fraudulent websites, fake social media profiles and misleading ads that may misuse official logos or endorsements.

These unauthorised GLP-1 injections can:

• Contain the wrong or no active ingredient

• Include harmful substances

• Deliver incorrect dosages

• Cause serious or unexpected side effects

• Interact dangerously with other medications

GLP-1 injections are prescription only and should only be taken under the supervision of a healthcare professional. Never buy them without a prescription or from unverified sources.

 If you suspect a falsified or unlicensed product

If you suspect that your medication may be falsified or unsafe, do not use it. Speak to your clinician or pharmacy immediately and report it to the MHRA Yellow Card Scheme.

In the UK, GLP-1 medicines are prescription-only medicines (POM). They should only be prescribed by a qualified healthcare provider and dispensed by a registered pharmacy.

How to use GLP-1 injections

Your clinician will explain and show you how to inject the GLP-1 medications . Always follow the instructions in the patient information leaflet and any training given by your clinician or pharmacist for your specific pen.

Step 1: Wash and Prepare

• Wash your hands thoroughly with warm soapy water or use hand sanitiser 

• Clean your injection site with warm water and soap or an alcohol wipe

• If using alcohol, let the area dry for at least 30 seconds to reduce stinging

Step 2: Check the Pen

• Make sure the pen is not expired or damaged

• Check that the medication is clear and colourless. Do not use the pen if the liquid is cloudy, discoloured or contains particles. Follow the advice in the patient information leaflet and contact your pharmacy or clinician for a replacement.

• Confirm that the dose on the pen matches your prescribed amount

Step 3: Attach the Needle

• Remove the protective seal from a new needle

• Attach the needle to the pen and twist it on tightly

• Remove both caps from the needle:

  • Keep the outer cap, as you’ll need it later for safe disposal

  • Discard the inner cap

Step 4: Prime the Pen (if instructed)

• Hold the pen upright and gently tap it to move any air bubbles to the top

• Press the button or turn the dial until a small drop appears at the tip of the needle

• If no medication comes out, you may be instructed to try again. If it still doesn’t work, contact us to have the pen changed

Step 5: Set Your Dose

• Turn the dial or dose selector to your prescribed dose

• Make sure the dose counter or window clearly shows the correct amount before injecting

Step 6: Inject the Medication

• Pinch the skin at the injection site, especially if you have less fatty tissue

• Insert the needle straight into the skin at a 90-degree angle

• Press and hold the injection button until the dose counter shows “0”

• After the counter reaches 0, continue to hold the needle in place for 5 to 6 seconds to ensure the full dose is delivered

• Remove the needle straight out of the skin

• If there’s any bleeding, press the site gently with a cotton ball

Step 7: Dispose of the Needle Safely

• Use the outer needle cap to safely cover the needle

• Unscrew the needle and dispose of it in a sharps container

• Put the pen cap back on and store it as directed (usually in the fridge)

• Never reuse needles

Where to inject GLP-1 medications

Step 1: Divide your abdomen and thighs into sections to create multiple injection areas. Rotate injection sites each week to avoid using the same spot repeatedly

Step 2: When injecting into the abdomen, make sure the new injection site is at least one finger width away from your previous site. It needs to be at least 5 cm from your belly button

Step 3: Turn the dose knob or dial until the correct dose appears in the dose window. Always confirm your prescribed dose before injecting

Step 4: Insert the needle into your skin and press the button or knob slowly to release the medication. Hold for about 6 seconds to ensure the full dose is delivered. After removing the needle, check that the dose window shows "0". If it does not, do not try to give more medicine. Follow the instructions in your medication’s patient leaflet and contact your pharmacist or clinician for advice, as this may mean the injection was not completed correctly.

What to expect when using GLP-1 treatment

When starting GLP-1 weight loss injections, it's important to know that it's a gradual process and this is designed to help your body adjust. GLP-1 medications typically start with the lowest dosage and are increased over several weeks. This gradual dosage increase helps your body adapt and improves tolerance to the medication.

One of the first changes many people notice is a reduced appetite. These medications work by slowing digestion and by sending stronger fullness signals to the brain, this can lead to smaller portion sizes and fewer cravings. Over time, this leads to a natural reduction in calorie intake without needing to follow a highly restrictive diet.

Weight loss tends to build gradually, with noticeable changes often appearing after a few weeks of consistent use. In clinical trials involving people who met specific criteria and used these medicines alongside diet and physical activity, many participants achieved at least 5% weight loss. These results may not reflect what any one individual will experience, and weight change can vary considerably.

It’s important to have regular reviews with your clinician throughout your treatment. These appointments help monitor your progress, manage any side effects you may experience and ensure the medication is working safely and effectively for you.

Common side effects

As your body adjusts to GLP-1 injections, you may experience some temporary side effects, particularly during the first few weeks or after a dosage increase. The most common side effects are gastrointestinal symptoms, including nausea, vomiting, diarrhoea, constipation, along with headaches and tiredness.

These side effects usually improve over time as your body becomes more used to the medication. Eating smaller meals, avoiding high fat or high sugar foods and staying well hydrated can help manage these side effects.

If any side effects become severe, prolonged or impact your daily living, speak to your clinician. They may adjust your dose or provide support to help ease symptoms during the transition period.

Long-term risks

Over time, some people may develop gastrointestinal issues, including gastroparesis. This is a condition where the stomach takes longer to empty  than normal. There is a possibility of developing a bowel obstruction, which can cause severe constipation, abdominal pain and vomiting. These conditions are uncommon but may become serious if left untreated.

There is also a known risk of pancreatitis (inflammation of the pancreas) and gallbladder problems, such as gallstones or gallbladder inflammation. If you experience ongoing stomach (abdominal) pain, especially with vomiting or fever, contact NHS 111 or your GP urgently. If the pain is severe or you feel very unwell, call 999 or got to A&E immediately.

If you’re using the oral contraceptive pill, it’s important to note that GLP-1 medicines can affect its reliability in two ways:

• Gastrointestinal side effects (such as vomiting or diarrhoea) can reduce absorption of the pill

• Tirzepatide (Mounjaro) has specific advice in its product information about a possible effect in how oral contraceptives are absorbed

Your clinician may recommend using a non-oral method or adding a barrier method (such as condoms), especially when starting treatment and after dose increases. 

An important consideration is that weight regain is possible after stopping GLP-1 injections, particularly if lifestyle habits such as diet and physical activity are not maintained. 

These risks are rare but having consistent reviews with your clinician are essential to ensure your treatment remains both effective and safe over time.

Switching between weight loss medications

Switching between different GLP-1 weight loss medications, such as moving from Wegovy to Mounjaro, can be done safely but only under the supervision of a clinician. Each medication may work slightly differently due to differences in how they target hormone receptors and their side effect profiles.

For example, some medications target a single hormone receptor, like Wegovy and Saxenda (GLP-1), while others, like Mounjaro, target two receptors (GLP-1 and GIP). This can affect how well the medication works and the potential side effects you might experience. Due to these differences, your clinician will guide you through the safest way to switch medications, including any necessary dose adjustments and monitoring to minimise any side effects.

Never change or stop your medication without first consulting your clinician to ensure the switch is safe and suitable for you.

Get support with weight loss management

If you’d like support with managing your weight, you can book a consultation with one of our clinicians. They will review your health, discuss lifestyle changes and, where appropriate, talk you through the full range of suitable treatment options.