Weight Loss Injections

Weight-loss injections are medications given as weekly self-injections using a pre-filled pen. They are prescribed for people who meet medical criteria for obesity or who have health conditions linked to their weight.

These treatments help regulate appetite and blood sugar, making it easier to maintain a calorie deficit and improve metabolic health. They are always prescribed under medical supervision and work best when combined with nutrition, activity, and behavioural support.

Most modern weight-loss injections act on hormones that regulate hunger and fullness. They mimic the action of GLP-1 (glucagon-like peptide-1) which is a natural hormone that helps control appetite, digestion, and insulin release. This slows the rate at which food leaves the stomach and helps you feel full for longer. Some newer treatments also act on GIP receptors, which may enhance these effects.

Typical results:

• Noticeable appetite change in 1–2 weeks
  
• Average 10–20% body-weight reduction in clinical studies (when combined with healthy habits) over 18 months

There are 3 main types of weight loss injection: GLP-1 receptor agonists (e.g. Semaglutide); Dual agonists (e.g. Tirzepatide); Older injection types (e.g. Liraglutide).

Let’s look at them in turn.

These medicines mimic the GLP-1 hormone to help reduce appetite and regulate blood sugar. They are usually taken once a week.

In studies, people using GLP-1 injections lost on average around 15% of their body weight after a year, with improvements in blood sugar and heart health markers.

In the UK, semaglutide is available under the brand name Wegovy. (Brand names are provided for educational purposes only. Medicspot does not promote any specific prescription-only medicine.)

Common side-effects of GLP-1 receptor agonists include: mild nausea, reflux, constipation, and fatigue – but they are usually temporary.

These newer treatments act on two hormone pathways (GLP-1 and GIP). They may help some people achieve 20–25% body-weight reduction, based on recent clinical trials. Tirzepatide is taken once weekly using a similar injection pen.

In the UK, tirzepatide is available under the brand name Mounjaro. (Brand names are provided for educational purposes only.)

Earlier GLP-1 medications such as liraglutide (Saxenda) require daily injections rather than weekly ones.

While liraglutide is effective, newer options like Wegovy and Mounjaro are now preferred because they last longer in the body and tend to produce greater weight loss.

When used correctly and combined with healthy habits, weight-loss injections can lead to steady, clinically meaningful results.

Typical progress pattern:

• Weeks 1–2: Appetite reduction and early satiety.
  
• Weeks 4–8: Noticeable weight loss begins.
  
• Months 3–6: Continued loss, often 10–15% of initial body weight.
  
• 12 months+: Maintenance phase and dose stabilisation.
  

Like any medication, weight-loss injections can cause side-effects. Most are mild and short-lived, especially during the first few weeks as your body adjusts.

Common side-effects:

• Nausea or reflux
  
• Constipation or bloating
  
• Fatigue
  
• Mild stomach discomfort
  

Weight-loss injections are usually prescribed for people who:

• Have a BMI of 30 or higher, or
  
• Have a BMI of 27 or higher with a related condition (such as type 2 diabetes, high blood pressure, or sleep apnoea).
  
• Are aged 18-74 and are resident in the UK.

These medications are not suitable for people who are pregnant, breastfeeding, or have certain medical conditions (such as pancreatitis), some mental health conditions, and eating disorders.

Weight-loss injections work best when combined with changes in eating habits, activity levels, and behaviour. Medicspot’s clinicians and health coaches support this by helping patients set realistic goals and build sustainable routines.

See our resources on Diet and Nutrition

See our resources on Activity and Exercise

See our resources on Behaviour Change

If you’re interested in learning whether weight-loss injections could be suitable for you, take our free, confidential assessment to find out more about your options.

Take your free weight-loss assessment

Learn more about Wegovy and Mounjaro, two licensed GLP-1 treatments available in the UK.

Brand names are provided for educational purposes only. Medicspot does not promote any specific prescription-only medicine.

Dr Adam Abbs is a GP and Medical Lead for Europe and UK for biomarker company Hurdle. An NHS-trained GP, he graduated from Hull York Medical School in 2010 with an MBBS, then worked across a range of specialties in Newcastle and Manchester. Dr Adam Abbs is SCOPE certified (the international gold standard for obesity management) and has a keen focus on personalised medicine and weight loss. He authored Medicspot’s Behaviour Change Course.

Dr Abby Hyams completed her medical training in Bristol and has been a GP for 19 years, spending many of those as a partner in an NHS practice in Hemel Hempstead. She has a particular passion for supporting patients with weight loss and promoting positive behaviour change, helping individuals build sustainable habits that improve their long-term health and wellbeing.

This article is for general information only and should not be used for the diagnosis or treatment of medical conditions. Medic Spot Limited has used all reasonable care in compiling the information but makes no warranty as to its accuracy. Consult a doctor or other healthcare professional for diagnosis and treatment of medical conditions. In the event of an emergency, please call 999 for immediate assistance.

There is no guarantee of a specific weight loss medication being prescribed. Clinicians will review your online questionnaire alongside other independently validated medical information about you and will recommend the most appropriate weight loss treatments for you based on your answers. In some cases, the clinicians may contact you for additional information. See Terms of Service for more information.