Introduction
Obesity affects over 1 billion people worldwide, driving risks for type 2 diabetes, cardiovascular disease, and more. GLP-1 receptor agonists like Wegovy (semaglutide) and dual GLP-1/GIP agonists like Zepbound (tirzepatide) have transformed weight management, with average losses of 15-20% in trials. Now, Roche enters the fray with CT-388, a once-weekly injectable that hit 22.5% weight loss in phase 2—outpacing Wegovy and matching Zepbound's elite performance.
This guide breaks down the trial data, mechanisms, comparisons, and implications for patients eyeing next-gen therapies.
What is CT-388 and How Does It Work?
CT-388 is a dual GLP-1/GIP receptor agonist developed by Roche after acquiring Carmot Therapeutics for $2.7 billion in 2023. Unlike single GLP-1 drugs such as semaglutide (Ozempic, Wegovy), which mimic glucagon-like peptide-1 to curb appetite and slow gastric emptying, CT-388 also activates GIP (glucose-dependent insulinotropic polypeptide).
Why dual action matters: GLP-1 reduces hunger via brain signaling and promotes insulin secretion. GIP enhances insulin response and may improve fat metabolism, potentially amplifying weight loss without plateauing early. Administered as a 24 mg weekly injection, CT-388 targets sustained effects over 48 weeks, as seen in the trial.
Mechanism Snapshot: GLP-1 slows digestion and signals fullness; GIP boosts energy expenditure and insulin sensitivity—together, superior satiety and metabolic shifts.
Phase 2 Trial Results: Breaking Down the Data
Weight Loss Achievements
In the 48-week phase 2 trial, high-dose (24 mg) CT-388 users lost an average of 22.5% body weight—no plateau observed. This exceeds Wegovy's 15-17% in similar STEP trials (e.g., STEP 1: 14.9% at 68 weeks) and aligns with Zepbound's SURMOUNT-1 results (22.5% at 72 weeks on 15 mg).
- Low dose (dose not specified): Solid losses, building dose-response evidence.
- Key edge: Continuous loss trajectory suggests potential for even greater results in longer trials.
Real-world translation: A 100 kg (220 lb) patient could shed 22.5 kg (50 lbs), transforming health markers like blood pressure and A1c.
BMI and Obesity Resolution
Remarkably, 54% of participants reduced BMI below 30 kg/m², escaping clinical obesity. Baseline BMIs were likely 35-40+, per standard trials. This outperforms Wegovy's ~30-40% non-obese responders and matches tirzepatide's profile, signaling CT-388's potency for profound metabolic reset.
Safety and Tolerability
CT-388 mirrored GLP-1 class effects: gastrointestinal issues (nausea, vomiting, diarrhea) were common but manageable, with low discontinuation rates. No new red flags emerged, akin to semaglutide's 5-7% dropout in trials. Long-term cardiac and GI safety will be phase 3 priorities, building on GLP-1 precedents like LEADER and SELECT trials showing CV benefits.
