Why Wegovy can stop working — or never seem to work — for some people

The biggest misconception: if it's not working, the medicine must be fake or wrong

A question our prescribers hear most weeks is: "Could my pen be faulty, or is there a better version I should be on?" It is a reasonable thing to wonder, but the answer is usually more nuanced. Wegovy is a prescription-only medicine dispensed through the licensed UK supply chain; counterfeit or degraded product is a real risk from unverified sellers, but it is not the first explanation when someone using a legitimate pharmacy sees slower-than-expected progress.

The more accurate framing is this: semaglutide genuinely does not work equally for everyone, and that is documented in the trial data. The STEP 1 study, published in the New England Journal of Medicine, reported an average weight reduction of around fifteen per cent over 68 weeks at 2.4mg, but averages conceal a wide spread. Some participants lost over twenty per cent; a meaningful minority lost very little. Biological differences in gut-hormone receptor sensitivity, metabolic rate, and genetics all contribute to that spread. None of those factors are visible from the outside, and none of them are the patient's fault.

The practical upshot: slower progress does not automatically mean the medicine is not working at all. It may mean the full effect has not yet accumulated, or that something addressable is limiting it. If you want to read more about the specific circumstances in which results can fall short, our page on when and why Wegovy can fail to deliver the expected results is a good place to start.

The reasons semaglutide may not work as well for some people

Several distinct patterns explain why Wegovy may not work for some individuals the way the trial data suggests it should.

Biological variation. GLP-1 receptor agonists work by mimicking a gut hormone that signals fullness to the brain. How responsive a person's receptors are to that signal varies. There is emerging research into genetic variants that affect GLP-1 receptor function, though this is not yet part of routine clinical practice in the UK.

Undertreated dose. The 0.25mg starting dose is designed to let the body adjust gradually, not to produce weight loss. Reaching 2.4mg (the licensed maintenance dose) typically takes around five months of stepwise titration. People who cannot tolerate dose increases, or who stay at a lower dose for other reasons, are unlikely to see the full effect. The NHS medicines page for semaglutide sets out the standard titration schedule and is worth reading alongside your Patient Information Leaflet.

Adherence and timing. Wegovy is a once-weekly injection. Missing doses, injecting late repeatedly, or storing the pen outside the refrigerator in conditions that damage the medicine can all reduce its effect. The pen itself is straightforward to use, but the routine matters.

Lifestyle factors. Semaglutide reduces appetite significantly in most people, but if calorie intake remains very high (or if a highly sedentary lifestyle offsets the deficit) weight loss can stall. The medicine works alongside a reduced-calorie diet and increased activity; it does not replace them. You can read more about what shapes results on our page about people on Wegovy and what affects their outcomes.

Other medical factors. Certain medications (including some antidepressants, corticosteroids, and antipsychotics) are associated with weight gain that can partially counteract the treatment. Untreated hypothyroidism, insulin resistance, and sleep disorders can do the same. A prescriber reviewing your full picture is the only way to identify these.

Does semaglutide not work for some people permanently, or can a non-response be addressed?

This is where the evidence gets more useful. For some people, slow progress at an early dose resolves completely once they reach a higher one. The pattern of minimal early loss can look like non-response when it is actually just early-stage titration. Giving a dose step four to eight weeks to show its effect (rather than judging at two weeks) changes the picture substantially.

For genuine non-responders at the full maintenance dose, current NICE guidance on semaglutide (TA875) recommends reviewing whether continuing is appropriate if less than five per cent of body weight has been lost after six months at the highest tolerated dose. That review is a clinical conversation, not a reason to stop abruptly without advice. Some people in this situation are switched to a different mechanism; tirzepatide, which activates two receptor pathways rather than one, has shown greater average weight loss in head-to-head trials and may be a more suitable option for those who have seen limited results with semaglutide alone. It is also worth knowing that branded alternatives are not the only consideration, and our page on Sandoz semaglutide explains how that licensed version fits into the picture for patients weighing up their options.

The cost of different treatment options is worth understanding before switching. Our Wegovy cost guide covers what legitimate private treatment typically involves, and how to think about price alongside clinical suitability rather than in isolation from it.

The short answer to whether non-response is permanent: sometimes yes, sometimes no. Distinguishing between the two requires a prescriber who knows your dose history, your weight trend, and your health picture. If you are questioning whether treatment is right for you, speaking to a clinician is more useful than stopping quietly. Explore your treatment options with our prescribers to work out what makes sense for your situation.