In short.
441 adults with obesity began a 60-week course of Tirzepatide at the maximum tolerated dose (10 or 15 mg per week). Those who completed the course — 378 people, with an average weight loss of around 22% — were then randomised into three groups for the next 52 weeks:
- Group 1: continue at the same full dose (10 or 15 mg)
- Group 2: reduce to 5 mg as a maintenance dose
- Group 3: switch to placebo (an "empty" injection)
A year later, the outcome depended sharply on what they did: those who continued the full dose preserved almost all of the weight they'd lost, those who halved the dose kept most of it, and those who fully stopped regained more than half their weight loss — often within months.
What did they study?
The defining question in obesity care has been the same for years: do you need to stay on this medication forever, or can you taper once you've reached your target? For Tirzepatide, that question hadn't been properly answered in a randomised trial — until now.
The researchers compared three strategies after participants had already successfully lost weight for over a year:
- Continue unchanged on the dose used to achieve the loss
- Reduce to a maintenance dose of 5 mg — a frequent patient request, potentially cheaper and better tolerated
- Stop entirely and see what the body does on its own
All participants received the same lifestyle support. From week 84 (six months after randomisation), anyone could receive rescue Tirzepatide if they regained over 50% of the weight lost — an important ethical detail, because it means the placebo group wasn't tracked indefinitely.
What did they find?
The three groups diverged sharply after a year. Average weight relative to the very start of the whole programme:
— Full dose
−21.9%
Almost all the loss preserved — less than half a kilo difference from the end of the weight-loss phase.
— Reduced to 5 mg
−16.6%
Some weight back, but most of the loss preserved. A good middle-ground option for those wanting to lower their dose.
— Placebo (stop)
−9.9%
More than half the loss regained — despite 67% of this group eventually receiving rescue medication.
Another way to look at the same data: how much of the original loss was preserved among people who reached a plateau?
96.5%
Continued at MTD
Almost all weight loss preserved — Tirzepatide remains effective long-term.
67.9%
Reduced to 5 mg
The majority of the loss preserved — a serious option for maintenance.
42.8%
Placebo (stopping)
Less than half preserved — clearly inferior to either active dose.
8 / 25 / 67%
Needing rescue therapy
Share of patients with ≥50% weight regain, in the three groups respectively.
Beyond weight, there were clear differences in other outcomes — blood pressure, glucose, lipids, waist circumference — which were better preserved in both active groups than in the placebo group.
What about side effects?
The side-effect profile was familiar for Tirzepatide — mainly gastrointestinal during the early dose-escalation period, and mostly mild to moderate: nausea (35%), constipation (31%), diarrhoea (24%), vomiting (17%). During the maintenance phase (weeks 60–112), side effects were considerably lower than during the build-up phase — an important insight: the body adjusted.
One death occurred during the weight-loss phase (before randomisation), considered unrelated to Tirzepatide. During the 52-week maintenance phase there were no deaths. Serious adverse events were rare and evenly distributed across groups.
What does this mean for you?
This may be the most practically useful trial yet for anyone starting or in the middle of a Tirzepatide programme. Three concrete lessons:
- Stopping is not a casual choice. Those who fully stop lose, on average, more than half of the result they achieved — often within months. This fits with what we already knew about obesity as a chronic condition: the body actively tries to return to its previous weight.
- A 5 mg maintenance dose is a serious option. If the full dose is too much, or you want to reduce costs, 5 mg preserves most of the loss. Not as well as continuing at MTD, but significantly better than stopping.
- Continuing at MTD gives the best outcome. Almost all weight loss is preserved, plus the cardiovascular gains (blood pressure, lipids, glucose).
At Lunaris Clinics, this is exactly the conversation we have with you during a programme: after 12–18 months, we look together at whether continuing, reducing, or carefully tapering best fits — based on your goals, your weight trajectory, and how you experience the treatment.
Important caveats.
— Only one year measured
The maintenance phase lasted 52 weeks. Whether a 5 mg dose still offers the same protection after 3–5 years cannot be inferred from this trial. For a chronic condition, this remains an important open question.
— Rescue therapy clouds the picture
Ethically justified, but 67% of the placebo group was offered Tirzepatide after ≥50% regain. The "true" effect of fully stopping without a safety net is therefore probably even worse than the numbers suggest.
— No participants with diabetes
As with previous SURMOUNT trials, people with type 1 or type 2 diabetes were excluded to keep the effect clean. For patients with both diabetes and obesity, the calculus may differ.
— Funded by Eli Lilly
The trial was funded by the manufacturer of Tirzepatide. That's standard for phase 3 research and doesn't necessarily compromise scientific quality — peer review and the Lancet editorial team see to that — but it's relevant to know.
— American population
Participants were recruited at 20 US centres. Median BMI was 40 — high. The findings should translate well to the Netherlands, but the typical Lunaris patient has a lower BMI.
— Original source
Horn DB, Aronne LJ, Wharton S, et al. Tirzepatide for maintenance of bodyweight reduction in people with obesity in the USA (SURMOUNT-MAINTAIN). The Lancet, published online 12 May 2026.
DOI: 10.1016/S0140-6736(26)00656-2 · ClinicalTrials.gov: NCT06047548 · Full publication subscriber-only; abstract openly available.
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