How Do Weight Loss Injections Work
Learn what to expect from GLP-1 weight loss injections, including how they work, appetite regulation, fullness signals and safety considerations. This guide also answers frequently asked questions about GLP-1 weight-loss medicine.
Medically reviewed by Danny Chu, HCPC-Registered Physician Associate (PA38670).
How Do Weight Loss Injections Work?
Disclaimer: The following information is provided for educational purposes only. Semaglutide (Wegovy) and Tirzepatide (Mounjaro) are prescription-only medicines. This page does not constitute an advertisement. Always consult a qualified healthcare professional before starting any medication. Terms and conditions apply.
Most modern weight loss medications work by targeting hormones involved in appetite and digestion. Some medicines act on a hormone called GLP-1. Others target both GLP-1 and GIP. These hormones help regulate hunger, fullness and blood sugar levels after eating.
When part of a balanced diet and healthy lifestyle, weight loss injections may support weight loss by:
- Reducing appetite
- Improving blood sugar regulation
- Slowing stomach emptying
- Reducing food cravings
- Supporting feelings of fullness for longer
A combination of these factors may lead to reduced calorie intake, contributing to gradual weight loss over time. Some people also find it easier to maintain healthy eating habits.
The National Institute for Health and Care Excellence (NICE) recommends injections only be used as part of a weight loss programme that includes:
- A reduced-calorie diet
- Regular physical activity
- Follow-up support
Note: Weight-loss medication should only be used under the supervision of a qualified healthcare professional.
Injection for Weight Loss in the UK
Interest in GLP-1- and GIP-based weight-loss medication has increased significantly in the UK in recent years.
- In 2025, researchers estimated that nearly 1 in 10 adults in Great Britain Jackson SE et al., BMC Med, 2026 had either recently used these medicines for weight loss or were interested in using them in the near future.
- Some patients may be eligible for support through NHS weight services or specialist weight management programmes, depending on local criteria and clinical need.
- NICE updated its guidance in 2025 to recommend structured follow-up and ongoing support after weight management treatment.
Types of Weight Loss Injections
Three main prescription weight loss injections are available in the UK.
Tirzepatide (Mounjaro)
Mounjaro contains the active ingredient tirzepatide. It works on both GLP-1 and GIP receptors, which help regulate appetite and blood sugar levels.
Semaglutide (Wegovy)
Semaglutide is a GLP-1 receptor agonist used as part of a specialist weight management programme.
Liraglutide (Saxenda®)
Liraglutide is another GLP-1-based weight-loss medication prescribed in some specialist weight management services.
Do Weight Loss Injections Work?
Clinical studies suggest that weight loss injections may support weight loss in some people when combined with a healthy diet and regular physical activity.
Results vary between individuals. Factors such as starting body weight, medical history, eating habits and activity levels can all affect outcomes. These medicines are usually intended to support long-term weight management rather than rapid weight loss.
Some studies have also linked weight reduction with improvements in weight-related health issues, such as:
- Abnormal blood fats
- Heart disease
- High blood pressure
- Obstructive sleep apnoea
- Cardiovascular disease
These types of weight loss treatments are not suitable for every patient. A healthcare professional will assess whether treatment may be appropriate based on your medical history and overall health.
Are Weight Loss Injections Safe?
Like all prescription medicines, weight loss injections can cause side effects.
Common side effects may include:
- Constipation
- Nausea
- Diarrhoea
- Stomach discomfort
- Vomiting
Some people may also experience low blood sugar, particularly if they are taking other diabetes medicines.
Regulation of Prescription Weight-Loss Medication in the UK
In the UK, prescription weight-loss medication is regulated by the Medicines and Healthcare Products Regulatory Agency (MHRA). These medicines should only be prescribed following an assessment by a qualified healthcare professional.
Patients should avoid buying weight-loss products from unregulated websites or social media sellers. Some products sold online may be unlicensed, unsafe or contain harmful ingredients.
Side Effects of Weight Loss Injections
Most side effects are mild to moderate and often improve over time as the body adjusts to treatment.
Who May Be Suitable for GLP-1 Weight-Loss Medication?
Weight loss injections may be considered for adults living with obesity or excess weight, particularly where weight-related health conditions are also present.
Eligibility may depend on factors such as:
- BMI
- Current health conditions
- Medical history
- Previous weight loss attempts
Treatment should be part of a broader weight-loss journey that includes healthy lifestyle changes.
FAQs
Frequently Asked Questions
Need More Information About GLP-1 Weight Loss Medications?
The most appropriate treatment depends on individual health needs, medical history and clinician assessment. Read our guide to the best weight loss injections available in the UK.
Weight loss injections are prescription-only medicines. Patients usually need an assessment with a healthcare professional before treatment can be prescribed.
The cost of medication varies depending on the treatment prescribed, dosage and weight-loss service.
Weight-loss injections should only be obtained from regulated providers following a medical assessment.
Note: Buying medication from unregulated websites or social media sellers may carry health risks.
Yes, some prescription weight-loss injections may be available through NHS weight services for eligible patients. Access depends on factors such as BMI, medical history and weight-related health conditions. A healthcare professional can advise on whether treatment may be appropriate as part of a weight-management plan. Alternatively, they might refer you to other NHS weight services to help achieve a healthy weight.
If you would like to discuss whether a prescription weight-loss injection may be suitable for you, Envigore's clinical team offers a free online eligibility assessment. An HCPC-registered prescriber conducts all our consultations.
Sources & Further Reading
At Envigore, we believe conversations about weight deserve understanding, support and reliable information without judgment. Clinical insight, patient perspectives and established medical research guide our content.
For additional context and transparency, readers can explore the medical resources and journal references included throughout this page.
Ahmad N, Alruwayyes A, Alarjani A, Tawhari A, Aldosri A, Alahmari A, Balaha M. GLP-1 receptor agonists for weight loss: A systematic review and meta-analysis of randomized controlled trials. Medicine (Baltimore). 2026 Mar 13;105(11):e47994. doi: 10.1097/MD.0000000000047994. PMID: 41824845; PMCID: PMC12991648.
Dawson SW, Le DQ, Tan EJ, Le LK. The regulation on the use of supplements for weight control: Case studies from Australia, the United States of America, and the United Kingdom. Health Policy Open. 2025 Feb 16;8:100136. doi: 10.1016/j.hpopen.2025.100136. PMID: 40084066; PMCID: PMC11905821.
Friedrichsen M et al. The effect of semaglutide 2.4 mg once weekly on energy intake, appetite, control of eating, and gastric emptying in adults with obesity. Diabetes Obes Metab. 2021. doi:10.1111/dom.14280.
Guo H et al. Comparative efficacy and safety of GLP-1 receptor agonists for weight reduction: A model-based meta-analysis of placebo-controlled trials. Obesity Pillars. 2025. doi:10.1016/j.obpill.2025.100162. PMC11840199.
Insights into the Mechanism of Action of Tirzepatide. Diabetes Therapy. Springer, 2025. doi:10.1007/s13300-025-01804-w.
Jackson SE et al. Prevalence of use and interest in using GLP-1 receptor agonists for weight loss: a population study in Great Britain. BMC Med. 2026. doi:10.1186/s12916-025-04528-7.
Ghusn W, Hurtado MD. Glucagon-like Receptor-1 agonists for obesity: Weight loss outcomes, tolerability, side effects, and risks. Obes Pillars. 2024 Aug 31;12:100127. doi: 10.1016/j.obpill.2024.100127. PMID: 39286601; PMCID: PMC11404059.
Dandamudi M, Lucena L, Gamarra-Valverde NN, Tripoli A, Ho VQT, Samaniego M, Pinilla J, Lopez M, Chamay S, Giorgi J, Barbagelata A, Kaplinsky E. Efficacy of GLP-1 Receptor agonists in treating Obstructive sleep apnea: A systematic review and meta-analysis of cardiometabolic and respiratory outcomes. Sleep Breath. 2026 Apr 24;30(2):138. doi: 10.1007/s11325-026-03681-4. PMID: 42029967; PMCID: PMC13109165.
Malhotra A et al. Tirzepatide for the treatment of obstructive sleep apnoea and obesity. N Engl J Med. 2024. doi:10.1056/NEJMoa2404881.
O’Connor, J. (2026). Weighting the evidence: a scoping review of UK regulation of the commercial weight-loss industry and its harms. Justice, Power and Resistance, 9(1), 132-158. Retrieved May 13, 2026, from https://doi.org/10.1332/26352338Y2025D000000057
People need support to keep weight off after treatment ends. (2025, August 5). NICE Website: The National Institute for Health and Care Excellence. https://www.nice.org.uk/news/articles/people-need-support-to-keep-weight-off-after-treatment-ends
Sodhi M, Rezaeianzadeh R, Kezouh A, Etminan M. Risk of gastrointestinal adverse events associated with glucagon-like peptide-1 receptor agonists for weight loss. JAMA. 2023;330(18):1795–1797. doi:10.1001/jama.2023.19574.
Urva S, Coskun T, Loghin C, Cui X, Beebe E, O’Farrell L, Briere DA, Benson C, Nauck MA, Haupt A. The novel dual glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 (GLP-1) receptor agonist tirzepatide transiently delays gastric emptying similarly to selective long-acting GLP-1 receptor agonists. Diabetes Obes Metab. 2020 Oct;22(10):1886-1891. doi: 10.1111/dom.14110. Epub 2020 Jul 13. PMID: 32519795; PMCID: PMC7539915.
About Your Clinical Team
This content was medically reviewed and approved by Danny Gian Hou Chu, a HCPC-Registered Physician Associate (PA38670), who oversees all prescribing decisions at Envigore.
All prescriptions are dispensed by Right Medicine Pharmacy, a GPhC-Registered Pharmacy (No. 9012382).
Nutritional guidance and lifestyle support are provided by Veronica Giudice, an HCPC-Registered Dietitian (DT26570) and British Dietetic Association member.
Last medically reviewed: May 2026