Are weight loss injections good for you — and what does the evidence say?

The biggest misconception: these injections are just a shortcut

The most common misreading of GLP-1 weight loss injections is that they are a cosmetic shortcut, something for people who haven't tried hard enough. The clinical reality is different. Obesity is a chronic condition shaped by hormones, genetics and environment, and the medicines in this class were developed to address a biological driver of it: the dysregulation of appetite-signalling hormones. Tirzepatide activates two receptors, GIP and GLP-1, which together slow gastric emptying and reduce hunger signals. Semaglutide targets the GLP-1 receptor alone. Both approaches are well-characterised in peer-reviewed research.

In the SURMOUNT-1 trial, adults taking tirzepatide at the highest dose lost an average of around 20–21% of their body weight over 72 weeks, while the STEP 1 trial reported around 15% average weight loss for semaglutide 2.4mg over 68 weeks, both published in the New England Journal of Medicine. Weight reduction at that scale carries measurable downstream effects on blood pressure, blood sugar, sleep apnoea and joint load. That is not a cosmetic outcome. If you are trying to work out whether weight loss injections are good or bad for people in your situation, that is precisely the kind of question a prescriber assesses before treatment begins.

If you want a clear breakdown of how the two licensed options compare, the weight loss injections overview covers the mechanism and trial data side by side.

What the benefits actually look like, and for whom

A question our prescribers hear most weeks is some version of: "But are these injections actually good for you, or are there hidden risks?" It is a fair question. The licensed eligibility criteria give a useful answer: UK prescribers can consider these medicines for adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related condition such as hypertension, dyslipidaemia, type 2 diabetes or obstructive sleep apnoea. Lower thresholds apply for some ethnic backgrounds under UK guidance.

Within those groups, the benefit-to-risk balance has been assessed and approved by the MHRA. NICE's appraisal of tirzepatide, TA1026, specifically recommends it for adults with a BMI of 35 or above and at least one weight-related comorbidity, noting the strength of the evidence base. For people who fall within the licensed criteria, the weight of clinical evidence suggests these medicines are genuinely beneficial. For people outside those criteria (someone with a BMI of 24 wanting to lose a few kilograms, for example) the evidence does not support their use, and the MHRA has been clear that these medicines are not assessed for cosmetic weight loss.

The weight loss injection guide goes into more detail on what the treatment process looks like from start to finish.

The side effects are real, here is how to think about them

Side effects matter, and glossing over them would be misleading. The most common are gastrointestinal: nausea, loose stools, constipation, indigestion and burping are all reported in trials, typically peaking shortly after a dose increase and settling over days to a couple of weeks as the body adjusts. Fatigue, headache and injection-site reactions are also reported. Most people find these tolerable, particularly when the dose is increased gradually by the prescriber.

Rarer but more serious risks include acute pancreatitis. In January 2026 the MHRA issued a Drug Safety Update highlighting this as a known but infrequent concern with GLP-1 medicines: severe, persistent stomach pain that radiates to the back, with or without vomiting, requires urgent medical attention. Full prescribing information is set out in the NHS tirzepatide page, which covers both common and serious side effects in plain language.

These medicines are not recommended during pregnancy, breastfeeding, or for anyone trying to conceive. They are not licensed for under-18s. Anyone with a history of medullary thyroid carcinoma or MEN2 should not take them. A prescriber works through these contraindications before treatment starts, that clinical step is not optional, it is what makes the prescription safe. You can report any suspected side effects to the MHRA at Yellow Card.

For a wider look at the trade-offs between the injectable and oral options now available, this comparison addresses the question directly.

How good are weight loss injections compared with other approaches?

Lifestyle intervention alone (reducing calories, increasing activity) produces meaningful results for some people but is difficult to sustain when appetite hormones are working against you. Diet-only approaches rarely achieve or maintain weight loss above 5–10% in large populations. The GLP-1 medicines reach average reductions two to four times larger in controlled trials, which is why they have changed clinical guidelines. For context, what makes a weight loss injection effective runs through the factors that determine how well any individual responds.

That does not mean injections are always the right tool. Orlistat, an older oral option, works through a completely different mechanism and is appropriate for some patients. The new oral semaglutide tablet is now MHRA-approved for weight management and may suit people who prefer not to inject. A prescriber considers the full picture: your BMI, health conditions, medicines you already take, and personal preference. The cheapest or most heavily promoted option is rarely the right starting point. If you are weighing up costs as well as clinical fit, the cheapest weight loss injections page sets out what price comparisons miss, and our free consultation is where that clinical conversation begins. Speak to our prescribers if you want a clear answer on whether any of these options fit your situation.