One clinical weight-loss result has been published for CT-388: a mean change of −4.7% to −8.0% at day 29, against −0.5% on placebo. That is four weeks, from a phase 1 trial in healthy volunteers. Every other figure you may see attributed to this drug is either that number stripped of its timescale or an extrapolation.
The published trial
A phase 1, double-blind, randomised, placebo-controlled study in otherwise healthy participants with overweight or obesity. Two arms of dosing were tested: single subcutaneous doses of 0.5 to 7.5 mg, and four once-weekly doses of 5 to 12 mg.
| Design | Phase 1, randomised, placebo-controlled |
| Population | Otherwise healthy adults with overweight or obesity |
| Duration | 29 days |
| Doses | Single 0.5–7.5 mg, or 4 weekly doses of 5–12 mg |
| Weight change | −4.7% to −8.0% across doses |
| Placebo | −0.5% |
Glycaemic measures improved both fasting and on an oral glucose tolerance test, and the pharmacokinetics supported once-weekly dosing.
Why 8% cannot be compared with 20.9%
This is the mistake the drug's coverage makes constantly, and it flatters CT-388 rather than the other way round.
| Drug | Weight loss | Measured at | Phase |
|---|---|---|---|
| CT-388 | up to 8.0% | Day 29 | 1 |
| Tirzepatide | 20.9% | 72 weeks | 3 |
| Semaglutide | 14.9% | 68 weeks | 3 |
| Orforglipron | 11.1% | 72 weeks | 3 |
Twenty-nine days against roughly five hundred. These are not the same measurement taken at different scales; they are different measurements. A drug that produces 8% in a month might end anywhere — higher than tirzepatide, or well below it — and a phase 1 trial is not designed to indicate which.
What the figure does say is that the effect appears early and at a useful size. Losing 8% of body weight in four weeks is not a marginal signal, and it is why the programme moved forward.
What the trial could not show
- Where the curve flattens. Every drug in this class slows down; none of them lose weight at their first-month rate indefinitely. When CT-388 slows, and at what level, is unknown.
- Whether it holds in patients rather than volunteers. The trial enrolled otherwise healthy participants, which is standard for phase 1 and not the population the drug is for.
- Responder rates. No proportions reaching 5%, 10% or 15% have been published.
- How it compares. No head-to-head against any approved drug is registered.
The reason to keep watching anyway
Two things, neither of them the 8%.
Roche is running phase 3. A phase 3 obesity programme costs hundreds of millions of dollars, and companies commit to that on internal data the public has not seen. Seven studies are registered and the lead ones are recruiting.
And the mechanism is a genuinely different bet. CT-388 is a signalling-biased agonist: engineered to activate GLP-1 and GIP while causing minimal receptor internalisation, so the receptors stay available. Most of the pipeline is adding receptors; this changes the quality of the signal at the two receptors tirzepatide already uses. If it works, it is a direction nobody else is taking. The detail is in the CT-388 overview.
The rest of the set
What is CT-388 is the short introduction, CT-388 side effects explains why no incidence figures exist, and the comparisons are vs Zepbound, vs Wegovy and vs Ozempic.
Scientific References
2 sources- 1
Chakravarthy MV, Rodriguez R, Hergarden A, et al.
Effects of CT-388, a once-weekly signaling-biased dual GLP-1/GIP receptor agonist, on weight loss and glycemic control in preclinical models and participants with obesity
Molecular Metabolism · 103 · 2026PMID: 41319798
NIH - 2
Jastreboff AM, Aronne LJ, Ahmad NN, et al.
Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)
New England Journal of Medicine · 387(3) · 2022PMID: 35658024
NEJM
References open in a new tab. Content is reviewed against peer-reviewed literature as part of our editorial policy.
About the author
Editor, Modern Weight Science
Claudiu Gheorghe is the editor of Modern Weight Science. He is not a physician. His role is to synthesize peer-reviewed studies, clinical-trial data, and FDA prescribing information into clear, plain-language explanations, and to make sure every factual claim on the site traces back to a cited source. Any decision about starting, changing, or stopping a medication belongs with a licensed clinician who knows your history.
Every claim is checked against peer-reviewed research through our review process and fact-checking policy.
Frequently Asked Questions
How much weight loss does CT-388 cause?
The single published clinical result is a mean change of −4.7% to −8.0% at day 29, against −0.5% on placebo, from a phase 1 trial in healthy participants with overweight or obesity. No longer-term efficacy data has been published, so where the curve goes after four weeks is unknown.
Is CT-388 better than Zepbound?
Nobody can say. CT-388's 8% was measured at day 29; tirzepatide's 20.9% at 72 weeks. Those are not the same measurement at different scales — a drug losing 8% in a month could end anywhere, and a phase 1 trial is not designed to indicate where. No head-to-head trial is registered.
Why is CT-388's weight loss figure so much lower than other drugs?
Because it was measured after four weeks rather than sixteen months. Every figure quoted for approved drugs comes from trials running 68 to 72 weeks. Comparing 29 days with 500 days understates CT-388 substantially, which is why the timescale has to travel with the number.
Has CT-388 been tested in a phase 3 trial?
It is in phase 3 and recruiting, with seven registered studies, but no phase 3 efficacy results have been published. The only published clinical data is the phase 1 trial. Roche committing to a phase 3 obesity programme is itself informative, since those cost hundreds of millions and are launched on internal data.
Was CT-388 tested in people with obesity?
The published phase 1 enrolled otherwise healthy participants with overweight or obesity, which is standard for a first-in-human study but is not the same as the patient population the drug is intended for. Whether the effect holds in people with obesity and related conditions is what the later trials exist to establish.
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Where to read next
Not medical advice. This guide is for general education only. GLP-1 medications, dosing, and treatment suitability are decisions for you and a licensed clinician who knows your full medical history.