Weight Loss Injections to Lose 1 Stone: What the Evidence Actually Shows

You've set yourself a one-stone target, here's how that maps onto the trial data

Picture this: you've done the research, you know roughly what you want to achieve, and a stone feels like a concrete, manageable goal. That clarity is useful. It also helps to know where one stone sits relative to what the medicines have actually produced in trials, so expectations are grounded in evidence rather than optimism.

In the SURMOUNT-1 trial, tirzepatide (Mounjaro) produced an average body-weight reduction of around 20–21% over 72 weeks at the highest dose, with some analyses reaching higher. For someone starting at 14 stone, that is roughly two and a half to three stone on average, well past the one-stone mark. The SURMOUNT-1 paper in the New England Journal of Medicine is worth reading if you want the full picture. Wegovy's STEP 1 trial reported an average reduction of around 15% over 68 weeks. Again, for most starting weights, a stone is crossed relatively early in that trajectory.

The phrase "on average" is doing real work in those sentences. Some people lose more, some less. Dose, duration, and lifestyle all shift where an individual lands. What the data does suggest is that for most people who reach maintenance doses and stay on treatment, a single stone is not an especially ambitious target, it is closer to a milestone on the way to something larger. How weight loss injections actually produce that change is worth understanding before starting.

Why one stone might arrive sooner than you expect, or later

Timing is the part people find hardest to predict. Both medicines start at a low dose and escalate gradually (Mounjaro begins at 2.5 mg and Wegovy at 0.25 mg) because the body needs time to adjust. That first pen is about tolerability, not maximum effect. Weight loss during the early weeks tends to be modest.

As the dose increases, appetite suppression deepens. Gastric emptying slows. Meals feel satisfying sooner. The cumulative effect on calorie intake, sustained over months, is what produces the meaningful numbers seen in trials. For many people, a stone falls somewhere in the three-to-six-month window once a therapeutic dose is reached, though this is a rough guide only. Starting weight matters: a heavier starting point tends to produce faster absolute losses even at the same percentage.

There are also factors that slow progress. Inadequate protein intake on a reduced-calorie diet, disrupted sleep, high stress, and sedentary habits all blunt the medicine's impact. The NHS guidance on weight management injections makes clear that these medicines work best alongside meaningful lifestyle changes, not instead of them. You can read NHS England's guidance on weight management injections for a thorough overview. A broader look at weight loss treatment options may also help you choose an approach that fits your life.

One practical habit worth building early: weigh yourself at the same time each week, on the same scales, before eating or drinking. It takes under a minute and strips out the day-to-day water fluctuations that otherwise make the trend impossible to read.

Who can actually access these medicines, and what the assessment covers

Both Mounjaro and Wegovy are licensed for adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related health condition, such as high blood pressure, high cholesterol, type 2 diabetes, or obstructive sleep apnoea. Lower BMI thresholds can apply for some ethnic backgrounds under UK licensing guidance. BMI alone does not guarantee a prescription; the prescriber looks at the whole picture, including other medicines, existing conditions, and anything that would make either treatment unsuitable.

There is also a useful distinction between the NHS and private routes. On the NHS, tirzepatide is being rolled out in phased cohorts based on BMI and the number of qualifying conditions, access is currently limited to those with higher BMI and multiple comorbidities, with the criteria widening gradually. Many people who want treatment now, or who sit just outside the current NHS criteria, turn to a regulated private pharmacy instead. If cost is a consideration, reading about what drives the price of weight loss injections helps set realistic expectations before you commit.

Certain groups cannot use these medicines: pregnancy, breastfeeding, and actively trying to conceive are all situations where neither Mounjaro nor Wegovy is recommended. The medicines are not licensed for under-18s. A history of conditions such as medullary thyroid carcinoma or certain gastrointestinal disorders requires careful prescriber discussion. The frequently asked questions section covers many of the common eligibility queries in more detail.

Side effects to factor into your planning

The most common effects are gastrointestinal: nausea, loose stools, constipation, indigestion, and burping sit at the top of the list for both medicines. They tend to be most noticeable in the days following a dose increase and usually settle within a week or two as the body adapts. Eating smaller meals, staying well hydrated, and avoiding very fatty food helps considerably.

There are rarer but more serious effects to know about. The MHRA flagged acute pancreatitis as an infrequent but potentially serious risk associated with GLP-1 medicines in a Drug Safety Update issued in January 2026: severe stomach pain that spreads to the back, with or without vomiting, warrants urgent medical attention rather than watchful waiting. You can report suspected side effects through the MHRA's Yellow Card scheme.

Some people also ask about hair thinning during the early months of significant weight loss, this is a recognised pattern with rapid calorie reduction rather than a specific drug effect, and it typically resolves. Whether weight loss injections cause hair loss is addressed separately. If you have questions about how the kidneys respond to treatment, our page on weight loss injections and kidney stones looks at the evidence in detail, and anyone specifically wondering whether weight loss injections can cause kidney stones will find a dedicated review of what the current research says about that risk.

The general overview of weight loss injection treatment pulls together the practical side of starting, and our clinical team reviews every consultation personally before any prescription is issued. If a one-stone loss is your starting point and you'd like to understand whether treatment is clinically appropriate for you, the place to begin is a free clinical assessment, no pressure, no commitment, just the information you need to make the right call.

Check your eligibility with a free consultation.