Retatrutide vs Tirzepatide (Mounjaro): Which GLP-1 Wins for Weight Loss? [2026 Data]

Retatrutide likely leads to more weight loss than tirzepatide—based on current trial results—because it targets three receptors (GLP-1 + GIP + glucagon) instead of two (GLP-1 + GIP).

Two important caveats:

1. There is no published head-to-head trial of retatrutide vs tirzepatide yet, so this is an indirect comparison.
2. Retatrutide isn’t FDA-approved (clinical trials only), while tirzepatide is FDA-approved for chronic weight management (Zepbound)—so tirzepatide is the practical choice today.

Weight loss results (numbers)

Retatrutide (investigational)

• Phase 2 (NEJM, 48 weeks, obesity): up to −24.2% mean weight change at 48 weeks (highest dose group).
• Phase 3 topline (TRIUMPH-4, 68 weeks, obesity/overweight + knee osteoarthritis): −28.7% mean weight change at 68 weeks on 12 mg (placebo about −2.1%).

Tirzepatide (FDA-approved as Zepbound for weight management)

• SURMOUNT-1 (NEJM, 72 weeks, obesity/overweight):
  • 15 mg: −20.9%
  • 10 mg: −19.5%
  • 5 mg: −15.0%
  • placebo: −3.1%

What that means: On pure “percent weight loss,” retatrutide’s reported averages (up to ~24% at 48 weeks and ~28.7% at 68 weeks in TRIUMPH-4) are higher than tirzepatide’s ~21% at 72 weeks in SURMOUNT-1—again, not head-to-head and across different study populations.

Mechanism differences (GLP-1 vs GIP vs glucagon)

Tirzepatide = GLP-1 + GIP (dual agonist)

• GLP-1: reduces appetite, increases satiety, slows gastric emptying.
• GIP: incretin signaling that can complement GLP-1 effects and improve metabolic outcomes.
  Tirzepatide targets two receptors (GIP + GLP-1).

Retatrutide = GLP-1 + GIP + glucagon (triple agonist)

Retatrutide adds glucagon receptor activity on top of GLP-1/GIP. In theory, that extra pathway can contribute to additional fat loss via energy expenditure / metabolic effects—one reason the weight-loss numbers look so large in trials.

Who should choose which

Choose tirzepatide if…

• You want the best available weight-loss option you can actually get now via prescription.
• You want FDA-approved labeling, standardized dosing, and established access paths.

Choose retatrutide if…

• You’re eligible and willing to join a clinical trial (and accept you might be randomized).
• Your priority is potentially maximal weight loss based on early data—under research monitoring.

Don’t do this: try to “buy retatrutide” online. It’s not approved, and “research” products are not a safe workaround.

If you want results now, your fastest path is a clinician-supervised tirzepatide plan (it’s FDA-approved for weight management).
If you’re aiming for “next-gen” and can wait, look for retatrutide clinical trials near you and apply.

If you tell me what site this is going on (and your affiliate partner you’re sending people to), I’ll write a high-converting CTA block + FAQ schema that’s compliant and optimized for “retatrutide vs tirzepatide” and “which is stronger” queries.