Women weighed six months into an online tirzepatide program had lost 15.5%; the study had no comparison group

Weight-loss injections are no longer something only a hospital clinic hands out. A growing share are bought from online services, and the buyers are mostly women, representing the majority of users outside clinical trials. The large trials that tested these drugs’ effects on heart disease, the authors point out, enrolled mostly men. How well those services work has largely been a matter of what the companies say.

A study published on October 16 in Nature Medicine puts numbers on one of them, with a large caveat attached. Researchers led by John Deanfield of University College London followed 8,127 women in the UK who started a weight-loss medicine, almost always tirzepatide, through a structured online program over the winter of 2024 to 2025. Six months later, the women still being weighed had lost an average of 16.1 kilograms, or 15.5% of their starting weight, and 91% were still on treatment. There was no comparison group. Every woman in the study took the medicine and paid to join, and two of the authors work for the companies that ran the program. The study can describe what happened to these women, but it cannot say how much of it the program achieved.

What the online tirzepatide program involved

Tirzepatide, sold in the UK as Mounjaro, is a once-weekly injection that copies the action of two gut hormones. One of them, glucagon-like peptide-1, or GLP-1, gives the whole drug class its name. In its main weight-loss trial, known as SURMOUNT-1, tirzepatide produced substantial and sustained reductions in body weight.

The program in the study was run by two companies, eMed Healthcare UK and SheMed, and it asked a good deal more of its customers than an order form does. Women aged 18 to 80 with obesity, or overweight with a weight-related condition, enrolled online, had their identity and weight confirmed on a supervised video call, and posted back a finger-prick blood test from home before anything was prescribed. From then on they logged their weight weekly, had weekly live-video check-ins with trained proctors, who are not clinicians, and filled in a monthly questionnaire that had to be completed before a refill was approved. Once a month a clinician reviewed their progress and decided whether to raise the dose. A pooled team of 25 general practitioners, with pharmacists and nurse practitioners, handled the clinical side. The women paid a fixed fee covering the medicine, the blood tests and the support, and the provider partly subsidized it during the study.

Screening shed a lot of people along the way. Of 16,121 who met the first eligibility checks, 4,025 never completed the baseline blood test and 308 were turned away after a clinician reviewed their results, which left the 8,127 who received a prescription. Nearly all started on the lowest tirzepatide dose. Their average starting weight was about 104 kilograms, 95.5% had obesity, 88% were white, and a little over a third lived in the two most deprived fifths of UK neighborhoods.

How much weight the women lost in six months

Of the 7,297 women weighed at six months, 99.3% had lost weight. Average weight fell from 104.6 kilograms to 88.6 kilograms, a mean absolute reduction of 16.1 kg that came to 15.5% of starting weight. Almost all, 96.1%, lost at least 5% of their weight; 83.1% lost at least 10%, about half lost at least 15%, and 22.4% lost a fifth or more. More than half of the six-month loss came in the first three months.

They got there on modest doses. The average tirzepatide dose at six months was 9.5 mg a week, well short of the 15 mg maximum, because clinicians were told to hold off raising it for anyone already losing at least 2 kilograms a month or troubled by side effects. Weight loss was similar across starting weights and across richer and poorer neighborhoods. It was slightly smaller in older women, and in women who were not white, at 13.5% against 15.8% for white participants.

Not everyone stayed the course. 698 women, 8.6%, stopped treatment before six months, and by their last weigh-in they had lost much less: an average of 5.4 kilograms, or 5.4% of their weight. Women who completed the six months had lost 16.1 kilograms, or 15.6%, at their final weigh-in. Almost half of those who stopped had still shed at least 5% before they did.

Blood sugar, cholesterol and side effects in the program

Blood tests at six months, available for about four in five women, moved in the expected direction. Average HbA1c, a blood test that reflects blood sugar over recent months, fell from about 5.5% to 5.2%. Of the 155 women whose starting reading was in the diabetes range, 84.5% had normal readings at six months, as did 96.3% of the 567 with prediabetes. Total cholesterol, LDL cholesterol and triglycerides all fell. HDL, the so-called good cholesterol, dipped slightly, a pattern the authors say is common during active weight loss and tends to reverse once weight stabilizes. Few women reported starting cholesterol or diabetes medicines during the study, so those are unlikely to explain the changes, although that information was self-reported.

Side effects were common. 62.7% of women reported at least one, mostly gastrointestinal, and among them the worst episode was mild for 36.8%, moderate for 55.4% and severe for 7.7%. Among the 5,092 women who reported side effects, those who used the program’s symptom-management package, which offered over-the-counter remedies and dietary advice, were less likely to stop treatment: 189 of 3,778 (5.0%) stopped, against 97 of 1,314 (7.4%) who did not use it. Eleven women reported a pregnancy, and all of them stopped the injections at once. The authors recorded no serious treatment-related adverse events over the six months.

Why one program with no comparison group is hard to judge

A trial assigns people by chance to the treatment or to a placebo, so the groups differ only in what they were given. This study had one group, all on tirzepatide, all in the program. It therefore cannot separate three things that might each have helped: the medicine itself, the monitoring and support around it, and the women’s own determination. The authors say so plainly: “Causal attribution to pharmacotherapy cannot be definitively established, and residual confounding is possible.”

The way people entered the study also tilts toward good results. Paying for a program screens out those who cannot afford it, and the authors acknowledge that willingness to pay for a structured health program may itself select more motivated participants, which could flatter both the weight loss and the 91% retention. A quarter of the women who passed the first checks dropped out before their first blood test, and nobody knows how they would have fared. The analysis counted only women with measurements at both ends, though the authors report that a statistical reweighting to allow for the missing data gave similar answers.

The program’s operators are also part of the study. Rachael Joy is an employee of SheMed and Matthew Noble of eMed, the two companies that co-operated the program, and Deanfield has received consulting fees from eMed. The work was funded by a grant from a US charitable trust administered through University College London, and the funder had no role in the analysis.

How the women’s results compare with tirzepatide trials and other online services

The benchmark is SURMOUNT-1, a trial funded by the drug’s maker, Eli Lilly, in which 2,539 adults without diabetes were randomly assigned to tirzepatide or placebo for 72 weeks. By week 72 the mean percentage change in weight was a loss of 15.0% to 20.9% depending on dose, against 3.1% with placebo. The program’s 15.5% at six months, the authors write, aligns with early phase trajectories observed in the trials, and it was reached at lower doses. Whether these women would keep losing weight and reach the trial’s 72-week figures is beyond what a six-month study can show.

Other online services report broadly similar numbers. A UK prescribing service run by HeliosX found an average loss of 13.5% at 6 months among more than 270,000 people who started tirzepatide, and 17.4% at 12 months among the smaller group still reporting weights. All of that study’s authors were HeliosX employees and the company sells tirzepatide, so it has the same weakness of a provider studying itself. Its customers also reported their own weights, where the women in the Nature Medicine study had theirs confirmed on video at the start.

Staying on treatment is where the program looks most unusual. In US health records covering 125,474 adults who started a GLP-1 drug for weight, 64.8% of those without type 2 diabetes stopped within a year. The figures are not directly comparable, since the US study ran longer, defined stopping differently and included all comers, but the gap is wide. Deanfield’s team argues that the checks and follow-up built into their program set it apart from earlier platforms that operate as transactional prescribing services with little monitoring.

That fits what reviewers of the wider field describe. Sherry Pagoto and Richard Bannor, surveying digital obesity care in Current Obesity Reports this year, note that direct-to-consumer telehealth companies proliferated to meet the rapidly rising demand for these medicines after 2021, and that low engagement is a persistent problem with digitally delivered programs. Keeping nine in ten women on treatment for six months stands out against that record, provided the figure holds outside a paying, motivated group.

What the women’s program study leaves out

Six months is the opening chapter of a treatment many people expect to take for years. The SURMOUNT-4 trial showed what can follow. Adults who had lost about a fifth of their weight on tirzepatide and were then switched to a placebo regained 14.0% of their weight over the next year, while those who stayed on tirzepatide lost a further 5.5%. The trial’s authors concluded that withdrawing tirzepatide led to substantial regain of lost weight. The authors of the new study acknowledge that stopping these medicines is frequently associated with weight regain, and their data say nothing about it.

The women were mostly healthy, mostly white and all female, and the authors caution against applying the results to people who need the medicine because of serious obesity-related complications. Blood pressure and waist size were not measured. Medical histories and medicines were self-reported and not checked against health records, and some blood results went missing because of the home finger-prick kits.

What the results mean for online GLP-1 prescribing

England’s National Institute for Health and Care Excellence, known as NICE, recommends tirzepatide on the NHS only for adults with a BMI of at least 35 and at least one weight-related condition, and it is being introduced in phases. NICE also advises deciding whether to continue when less than 5% of the initial weight has been lost after six months at the highest dose a person can tolerate. Women outside those rules can pay privately instead, as every woman in this study did.

The authors conclude that digitally enabled care models “may provide a viable and scalable strategy to extend access to incretin-based pharmacotherapy as demand for obesity treatment continues to expand.” Their data back a narrower point: a structured online service delivered the medicine to thousands of women, monitored them remotely and kept most of them on it for six months. Whether such a service suits a particular person, and at what dose, is assessed by their doctor. Do not stop or change a prescribed medicine without talking to your doctor.

The open questions are whether the program did better than the same injections with less support, and what the scales will read a year from now.