Are Weight Loss Injections Safe? Side Effects & Risks

23 October, 2025  |  Jabbar Ali - MPharm

Weight loss injections have become one of the most popular medical treatments for people struggling to lose weight through diet and exercise alone. In the UK, medications such as Wegovy, Mounjaro and Saxenda are available under medical supervision to support safe and effective weight management. But the same questions still often come up:

• Is Wegovy safe?
• Is Mounjaro safe?
• Is Retatrutide a safer alternative?

This guide brings together everything you need to know about weight loss injection safety in one place: how these treatments work, the common and less common side effects (including the infamous 'eggy burps'), who is and is not suitable, and where new treatments like Retatrutide fit in.

How weight loss injections work

Weight loss injections typically contain active ingredients like semaglutide or tirzepatide. These medications mimic a natural hormone called GLP-1 (glucagon-like peptide-1), which helps regulate appetite and blood sugar levels. By activating GLP-1 receptors, these injections can:

• Slow down digestion, helping you feel fuller for longer
• Reduce appetite and food cravings
• Improve blood sugar control
• Support gradual and sustainable weight loss

The most well-known options available in the UK are Wegovy (semaglutide), a once-weekly injection that mimics the GLP-1 hormone to help you feel full for longer, and Mounjaro (tirzepatide), which works on both GLP-1 and GIP receptors for a dual effect on appetite control and metabolism. Both are available through licensed online pharmacies like IQ Doctor, where prescriptions are issued following an online consultation with a qualified prescriber.

When used alongside a healthy diet and regular exercise, weight loss injections can lead to significant results, often more effective than lifestyle changes alone.

Are weight loss injections safe?

Put simply, yes. When prescribed and monitored by a qualified healthcare professional, weight loss injections are considered safe for most people. However, as with any medication, there are potential side effects and considerations to keep in mind.

While clinical trials have shown that Wegovy and Mounjaro can lead to significant weight loss, often 10-20% of body weight over time, the safety of these medications depends on several factors, including your medical history, lifestyle and current medications.

Safety largely depends on:

• Proper medical assessment: not everyone is suitable for these treatments. Individuals with certain health conditions may need alternative options.
• Correct dosage and usage: following medical guidance ensures optimal results and reduces risks.
• Lifestyle support: diet, exercise and behaviour changes play a key role in long-term success.

To keep your treatment as safe as possible - always follow the prescribed dose, never combine multiple GLP-1 medications, eat smaller balanced meals to reduce nausea, and avoid alcohol, which can worsen side effects.

At iQ Doctor, all prescriptions are reviewed by UK-registered clinicians who ensure that the treatment is safe and suitable for you.

Common weight loss injections side effects

Most side effects are mild to moderate and tend to improve over time as your body adjusts to the medication. Common weight loss injection side effects include:

• Nausea or vomiting
• Constipation or diarrhoea
• Stomach discomfort or bloating
• Fatigue
• Mild headaches
• Loss of appetite
• Sulphur or 'eggy' burps (more on these below)

For the full list of common and uncommon side effects for your specific medication, always check the patient information leaflet. You can find the official leaflets for Mounjaro and Wegovy on the EMC website, which set out exactly how frequently each side effect occurs.

Why do weight loss injections cause eggy burps?

If you have started Mounjaro or another weight loss injection and noticed strange 'eggy burps', you are not alone. Sulphur burps are caused by hydrogen sulphide gas in the digestive tract. This gas naturally occurs when your body breaks down proteins or when food sits in the stomach longer than usual, both of which can happen on these medications. Here's why:

• Delayed stomach emptying: these medications slow down how quickly food leaves your stomach, which can lead to fermentation and gas build-up.
• Changes in gut bacteria: an altered digestive system may temporarily shift your gut microbiome, increasing sulphur gas.
• High-protein diets: many people on weight loss injections eat more protein to preserve muscle, which can produce more hydrogen sulphide.
• Dehydration or constipation: both can worsen digestive odours and slow transit time.

Eggy burps are considered a minor side effect and often resolve as your body adapts. To reduce them, try eating smaller meals, staying well hydrated, temporarily cutting down on sulphur-rich foods (eggs, onions, garlic, broccoli and red meat), limiting fizzy drinks, staying gently active after meals, and asking your doctor about probiotics. If symptoms persist, your prescriber may suggest adjusting your dose or reviewing your diet plan.

Less common and serious side effects

More serious side effects are rare but can include pancreatitis, gallbladder issues or allergic reactions. Always consult your prescriber immediately if you experience severe or persistent symptoms.

Less common but more significant side effects can also include gallstones, low blood sugar (especially in diabetic patients using other glucose-lowering medication) and injection site irritation. You should contact your healthcare provider if you experience persistent vomiting or dehydration, intense abdominal pain, an inability to keep food down, or severe constipation or diarrhoea. These could be signs that your dose needs adjustment.

What are UK patients saying?

Wegovy and Mounjaro reviews in the UK suggest that many users experience steady and consistent weight loss, often reporting reduced cravings and improved confidence. However, most reviews also mention mild nausea or digestive upset during the first few weeks, something that typically subsides as the body adapts. Users who combine weight loss injections with a calorie-controlled diet and regular exercise tend to see the most sustainable results.

Are weight loss injections suitable for everyone?

Weight loss injections are generally recommended for adults with:

• A BMI of 30 or higher, or
• A BMI of 27 or higher with a weight-related health condition (e.g. high blood pressure, type 2 diabetes).

They're not suitable for those who are pregnant, breastfeeding, or have certain medical conditions such as thyroid disease or pancreatitis.

If you're unsure whether you qualify, you can take an online consultation with iQ Doctor to see if the treatment is right for you.

What about Retatrutide? The next weight loss injection

Retatrutide is a new experimental medication being researched as a potential weight loss treatment. Developed by Eli Lilly (the same company behind Mounjaro), Retatrutide is part of a new class of weight loss medicine referred to as triple agonists. It targets three key hormone receptors in the body: GLP-1, GIP and glucagon. By stimulating all three, Retatrutide aims to help regulate appetite, blood sugar and metabolism, and early trials suggest it may produce stronger effects on fullness and energy expenditure than current GLP-1 medications.

Late-stage trial results have been striking, with average body weight reductions approaching 29% at the highest dose in Phase 3 data reported in late 2025, and further trial readouts and regulatory submissions expected through 2026. Retatrutide is widely anticipated as the next major weight loss treatment.

However, Retatrutide is not yet approved by the Medicines and Healthcare products Regulatory Agency (MHRA) and is not legal for sale or prescription in the UK. Any websites or sellers claiming to offer Retatrutide for purchase in the UK are operating illegally and may be selling unregulated or counterfeit products, which can be dangerous. Until it is licensed, the safest options remain the MHRA-approved treatments already available: Wegovy and Mounjaro, both prescribed through registered UK pharmacies like iQ Doctor.

We will update this guide as soon as Retatrutide receives UK approval.

iQ Doctor delivers the bottom line

Weight loss injections can be a safe and effective option for managing weight when used responsibly and under medical supervision. While mild side effects can occur, they're generally well tolerated, especially when the medication is started at a low dose and gradually increased. If you're considering weight loss injections in the UK, iQ Doctor provides a secure, doctor-reviewed service that ensures your safety from consultation to delivery.

iQ Doctor is a registered UK pharmacy that specialises in medical remedies for weight loss (including Wegovy and Mounjaro), erectile dysfunction, hair loss support and much more. Whether you require over-the-counter relief, or prescription-only medication, the experts at iQ Doctor can assist.

If you have any questions about side effects or safety, get in touch with IQ Doctor's clinical team.

Our Clinical Authors

Written by

Jabbar Ali

MPharm Clinical Lead | GPhC Registration: 2205490

Medically reviewed by

Omar El-Gohary

CEO & Superintendent Pharmacist | GPhC Registration: 2059792

This page has been written by a registered UK pharmacist and reviewed by our clinical team to ensure it is accurate, clear and reflects current clinical guidance.

Last medically reviewed: 23 October, 2025

Last updated: 13 October, 2026