Should I Take Weight Loss Injections? A Practical Guide

Step 1: Start with your BMI and your health picture, not a headline

The first question a prescriber asks is not "do you want to lose weight", it is whether you meet the clinical criteria for a licensed medicine. In the UK, Mounjaro and Wegovy are licensed for adults with a BMI of 30 or above, or 27 or above if you have at least one weight-related condition such as high blood pressure, type 2 diabetes, high cholesterol, or obstructive sleep apnoea. Mounjaro and Wegovy are the two injections currently licensed here for weight management; nothing else in this category holds UK approval for that purpose.

A quick thing to do right now: use the NHS BMI calculator to confirm your number. It takes under a minute and tells you immediately which threshold applies to you. That one check does not make you eligible (the prescriber still assesses everything else) but it stops you going further down a path that does not fit your situation.

Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance, so if you are of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean heritage, the 2.5 kg/m² adjustment may mean you qualify at a lower number than you expect. Your prescriber will apply this correctly.

Step 2: Understand what these medicines actually do

GLP-1 receptor agonists (and in tirzepatide's case, a dual GIP and GLP-1 receptor agonist) work through gut-hormone pathways that regulate appetite and blood sugar. You feel full sooner. Meals feel satisfying on less food. Gastric emptying slows. None of this is willpower; it is biology. Weight is a health condition shaped by physiology, and these medicines work with that physiology.

Clinical trials give some idea of what to expect. In SURMOUNT-1, adults taking tirzepatide lost around 20–21% of body weight on average over 72 weeks alongside diet and activity changes. Semaglutide 2.4mg produced around 15% average reduction in the STEP 1 trial over 68 weeks. These are trial averages, not individual predictions, real results vary, and what affects results includes diet, activity, adherence, and your own physiology. The trial evidence is cited in NICE's appraisal of tirzepatide (TA1026) for anyone who wants to read the regulator's assessment directly.

The treatment starts at a low dose (2.5mg for Mounjaro) because that first pen's job is letting your system adjust, not delivering the full therapeutic effect. Titration happens gradually, guided by your prescriber.

Step 3: Weigh up the side effects honestly

This is where many people pause, and rightly so. Side effects are common, particularly in the early weeks. Nausea is the most frequently reported, followed by constipation, diarrhoea, indigestion, burping, and fatigue. For most people, these are most noticeable after starting or after a dose increase, and they tend to settle as the body adjusts. Eating slowly, keeping meals smaller, and staying well hydrated all help.

There are symptoms that warrant prompt medical attention: severe, persistent stomach pain that radiates to the back (with or without vomiting) can signal pancreatitis, an infrequent but serious side effect that the MHRA highlighted in a Drug Safety Update for GLP-1 medicines. The Yellow Card scheme exists so patients can report suspected side effects directly to the MHRA, and it is worth knowing about.

There are also situations where these medicines are not suitable: pregnancy, breastfeeding, or actively trying to conceive, and for anyone under 18. A history of certain conditions (including medullary thyroid carcinoma or pancreatitis) requires careful prescriber discussion. If you want a full picture of who should not take these medicines, this page covers the contraindications in detail.

Step 4: Think about the practical and longer-term commitment

Should you take weight loss injections long term? That is a live question in the clinical world too. Treatment duration is not fixed at the start, it is reviewed as you go. There is good evidence that stopping the medicine leads to gradual weight regain for many people, which is why ongoing prescriber review matters rather than a one-off decision. This is a medical treatment, not a short course.

Diet and activity still matter on these medicines. Protein adequacy, hydration, and keeping active all support the treatment and protect muscle mass as weight comes down. The foods that tend to work best alongside GLP-1 treatment are not dramatic, mostly sensible, higher-protein, lower-fat choices that sit more comfortably when appetite is reduced anyway.

Cost is also real. Private treatment is not inexpensive. A single transparent price that includes consultation, prescription, delivery and ongoing clinical support is what treatment through a regulated service looks like, there are no hidden fees to discover halfway through. For a prescription medicine, price is not the right measure of value on its own; clinical oversight, genuine supply chain, and someone to contact if something feels off are the things that matter.

If you are still weighing this up, our guide to whether weight loss injections are right for you is a good place to work through the decision before taking it further. Our prescribers review consultations the same day (a real clinician reads your answers, not software) and they can give you a clear, personalised view of whether this treatment fits your situation. Speak to our prescribers when you are ready.