Weight-Loss Injection Side Effects Explained

GLP-1 weight-loss injections are one of the most effective medical treatments for people who struggle to lose weight through lifestyle changes alone. These medications, including Mounjaro and Wegovy, help regulate appetite, stabilise blood sugar and support steady long-term weight reduction when used alongside healthy diet and exercise.Many of the benefits of these treatments have been demonstrated in large clinical studies [1][2].

This guide explains how GLP-1 weight-loss treatments work, who they are suitable for, expected results, possible side effects and how to use them safely.

What Are GLP-1 Weight-Loss Medications?

GLP-1 medications belong to a group of treatments known as GLP-1 receptor agonists, which copy the action of a natural hormone that helps control appetite, digestion and blood sugar levels [5].

GLP-1 treatments were originally created for type 2 diabetes and were later found to have significant weight-loss benefits in people without diabetes as well [4].

Examples of GLP-1 weight-loss injections include:

• Mounjaro (tirzepatide). This works on GLP-1 and GIP receptors.
  
• Wegovy (semaglutide). A weekly GLP-1 injection for weight loss.
  
• Ozempic (semaglutide). Licensed for diabetes but sometimes used off-label for weight management.
  

How GLP-1 Weight-Loss Injections Work

GLP-1 medications support weight loss in several clinically proven ways.

1. Reduced appetite

They slow the rate the stomach empties, which helps you feel fuller for longer and reduces snacking [5].

2. Fewer cravings

These medicines act on areas of the brain that regulate hunger and reward, which can reduce cravings and help control portion sizes [6].

3. Better blood sugar control

GLP-1 treatments stabilise blood sugar levels, helping prevent energy dips and reducing cravings for high-sugar foods [4].

4. Balanced hormonal response

They support a healthier insulin response, which can be helpful for people with insulin resistance [4].

5. Steady and sustainable weight loss

Weight typically decreases gradually. Most people notice the biggest changes once they reach a maintenance dose.

Expected Weight-Loss Results

Weight loss varies depending on the medication, the starting dose, adherence and lifestyle changes.

Clinical studies show:

• Wegovy can lead to an average reduction of about 15% of body weight over 68 weeks [1].
  
• Mounjaro can lead to an average reduction of around 20 to 22.5% at higher doses[2].
  

These results are higher than those seen with most traditional weight-loss medicines.

Weight tends to reduce slowly and steadily. Most progress happens once the correct maintenance dose has been reached.

Who Is Suitable for GLP-1 Weight-Loss Treatment?

GLP-1 injections may be suitable for people who:

• Have a BMI of 30 or above.
  
• Have a BMI of 27 or above together with a weight-related condition such as high blood pressure, high cholesterol or pre-diabetes.
  
• Have struggled to lose weight through lifestyle changes alone.
  
• Are not pregnant or breastfeeding.
  
• Are not taking medicines that could interact with GLP-1 treatments.
  
• Have no medical conditions that make these medicines unsuitable.

These criteria are based on recognised weight management guidance, including NICE recommendations for obesity management [3]

Suitability is carefully checked during the online consultation.

How to Use GLP-1 Weight-Loss Injections

Most GLP-1 injections are taken once a week. Each pen comes with clear instructions for safe and effective use.

Key points to remember:

• Inject into the stomach, thigh or upper arm.
  
• Rotate injection sites each week.
  
• Follow the recommended dose increase schedule.
  
• Do not increase your dose earlier than advised.
  
• Store the pens correctly. Most are refrigerated before first use.
  

If you miss a dose, follow the product guidance or contact the pharmacy team for advice.

Dosage and Titration Schedule

GLP-1 treatments start with a low dose so your body can adjust. The dose increases gradually over several weeks.

A typical titration might look like:

• Weeks 1 to 4. Starting dose.
  
• Weeks 5 to 8. Moderate dose.
  
• Weeks 9 to 12. Higher dose.
  
• Maintenance dose. The ongoing weekly dose that suits your response and tolerance.
  

Exact schedules vary between medications. Each product page will include full details.

Common Weight Loss Injection Side Effects

Most side effects are mild and improve as your body gets used to the medication.

Commonly reported effects include:

• Nausea
  
• Bloating
  
• Indigestion
  
• Diarrhoea or constipation
  
• Tiredness
  
• Reduced appetite
  
• Mild discomfort at the injection site
  

If side effects persist, dose adjustments or practical steps at home can help. Read our guide to the most common side effects of weight loss medications and how to manage them for further information.

When GLP-1 Weight-Loss Injections Are Not Suitable

These treatments are not suitable for everyone.

They are usually avoided if you have:

• A history of pancreatitis
  
• Severe digestive conditions
  
• Certain endocrine disorders
  
• Pregnancy or breastfeeding
  
• An allergy to any ingredient in the medication
  

Your online consultation will check all safety considerations before prescribing.