By Alwyn Fortune, RPS Wales Policy and Engagement Lead

Weight loss injections like semaglutide and tirzepatide have exploded in popularity recently, driven by celebrity endorsements and growth in their availability online. But along with this popularity has also brought confusion, misinformation and concerns about buying fake medicines online.

Here’s how these injections work, who they’re for and how to use them safely.

What are weight loss injections?

Weight loss injections are prescription-only medicines designed to support people who are overweight or living with obesity. They work by mimicking hormones that help regulate appetite and digestion, helping patients feel fuller for longer, reducing cravings and making it easier to eat less overall.

They’re not a quick fix and should always be used alongside lifestyle changes, such as a healthy diet and regular exercise.

How do weight loss injections work?

Different weight loss injections act on different hormones, including:

• Semaglutide (Wegovy) and liraglutide (Saxenda, Biolide, Nevolat) mimic GLP-1, a hormone released after eating, which tells the brain you're full, slows digestion and helps reduce appetite.
• Tirzepatide (Mounjaro) mimics both GLP-1 and GIP, two hormones that work together to regulate appetite and improve how the body breaks down fat and sugar.

Which weight loss injections are approved for weight loss?

Only certain products are licensed for weight management in the UK, including:

• Wegovy (semaglutide)
• Saxenda, Biolide and Nevolat (liraglutide)
• Mounjaro (tirzepatide)

These are licensed in the UK for weight loss only in adults with a Body Mass Index (BMI) of 30 or over, or a BMI of 27 or more if they have weight-related conditions such as high blood pressure or type 2 diabetes.

Similar medicines, such as Ozempic, are only approved for treating type 2 diabetes and should not be used for weight loss unless prescribed off-label and used under medical supervision.

How effective are weight loss injections?

Results vary by person and product. On average, people lose between 8 – 20% of body weight, depending on the medicine used and how well they stick to lifestyle changes. 

Most people can expect to lose at least 5% of their body weight after six months of treatment. If this doesn’t happen, your healthcare professional may review whether it’s suitable to continue.

Are there side effects of weight loss injections?

Like all medicines, weight loss injections can cause side effects, especially when starting treatment or increasing the dose. Common side-effects include:

• Nausea
• Diarrhoea
• Constipation
• Stomach pain
• Headaches
• Dizziness
• Fatigue

People with diabetes may also experience low blood sugar, especially if taking insulin or other diabetes medicines. Healthcare providers may adjust the medication if needed.

Less common but serious risks include pancreatitis and gallbladder problems, which healthcare providers should discuss with patients before starting treatment.

Accessing weight loss injections safely

Weight loss injections should only be used under the care of a qualified healthcare professional. They should not be bought from unregulated websites or social media, as fake products can pose serious health risks.

If considering an online provider, make sure the pharmacy is UK-based, licensed and registered with the General Pharmaceutical Council (GPhC). Look for the official green pharmacy logo shown to the right on their website, which links to the GPhC’s register.

Some of these medicines are also available on the NHS, but usually only through referral to a specialist weight management service. Access is based on strict criteria set by NICE, and availability may vary by location.

These medicines can be accessed privately but should be used only after a thorough medical consultation with an appropriate healthcare professional, together with ongoing monitoring and support to ensure effectiveness and safety.

Considerations on misuse and demand

Weight loss injections can be an effective option for people who are struggling to lose weight and have tried other methods without success. But they’re not suitable for everyone and should always be used safely and with support from a healthcare professional.

If you’re considering treatment, talk to your GP or pharmacist about your options and whether these medicines are right for you.

For more detailed information on accessing weight loss medicines, read this NHS England guide.

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