Roche's CT-388 shows 22.5% weight loss, company plans phase 3 obesity trials

Roche reported on Jan. 27, 2026 that its experimental weight-loss drug CT-388 produced 22.5% placebo-adjusted weight loss at 48 weeks in a mid-stage trial, and the company said it will begin two phase 3 obesity trials this quarter ^[1][2].

CT-388 is a dual GLP-1/GIP receptor agonist, targeting the same two gut-hormone receptors as Eli Lilly's Zepbound ^[1]. Roche acquired it through its $2.7 billion purchase of Carmot Therapeutics in 2023, and it is given as a once-weekly injection ^[1][2].

The phase 2 trial enrolled 469 people with obesity or who were overweight, testing three subcutaneous doses against placebo ^[1]. The main endpoint was percent change in placebo-adjusted body weight from baseline to week 48. The highest dose studied, 24 mg, produced 22.5% loss ^[1]. Under a different analysis, called the treatment-regimen estimand, placebo-adjusted weight loss was 18.3% ^[1].

Roche said it did not detect weight loss plateauing by the 48-week mark ^[1][2]. Among patients on the highest dose, 95.7% lost more than 5% of their body weight and 26.1% lost more than 30% ^[1]. More than half of participants saw their obesity resolve, compared with 13% in the placebo group, and 73% of those who entered the trial with pre-diabetes had normal blood glucose at week 48, versus 7.5% on placebo ^[2].

Roche described CT-388 as well tolerated, with the majority of gastrointestinal-related adverse events mild to moderate and generally consistent with the incretin class of medicines ^[1]. In the treatment arm, 5.9% of patients discontinued treatment, compared with 1.3% in the placebo group ^[1][2]. Roche did not give specifics of the dropouts and said more data would come at an upcoming medical meeting ^[2].

Cross-trial comparisons are not head-to-head. Zepbound's 15-mg dose was tied to a 20.9% reduction in body weight after 36 weeks ^[1]. Analysts at William Blair said CT-388 appears comparable to Zepbound, and analysts at ODDO BHF called the results a material pipeline upgrade for Roche, adding that CT-388 could sit in the top efficacy tier of weight-loss drugs if phase 3 replicates the finding ^[1]. Roche Chief Medical Officer Levi Garraway said the "robust weight loss combined with a well-tolerated safety profile" reinforces the company's confidence as it advances to phase 3 ^[1].

Why it matters for patients

CT-388 is not approved by the FDA and is not available by prescription. The numbers released so far come from a phase 2 study, and the full dataset has not been published ^[1][2]. For people already taking an approved GLP-1 medicine such as Novo Nordisk's Wegovy or Lilly's Zepbound, this readout does not change today's options ^[2].

Nausea is the main driver of discontinuation from existing weight-loss products, and Roche is combining CT-388 with petrelintide, a long-acting amylin analog from Zealand Pharma that works differently than currently approved GLP-1 medicines ^[1]. Whether that combination reduces side effects has not been reported; a study of the two drugs together is expected to begin in the first half of this year ^[2].

Whether a new high-efficacy competitor would change US prices or insurance coverage has not been reported.

What happens next

Roche confirmed it will take CT-388 into a pair of phase 3 obesity studies this quarter, the first three months of 2026 ^[1]. The company first outlined its phase 3 ambitions for the asset at its Pharma Day in September 2025 ^[1].

Roche and partner Zealand Pharma are expected to initiate a combination study of CT-388 and petrelintide in the first half of 2026 ^[2]. Roche has said the full phase 2 data will be presented at a future medical conference but has not disclosed which meeting or when ^[1][2]. Morningstar Equity Research does not expect CT-388 to reach the market until 2029 ^[2].