Key Takeaways
  • Semaglutide (Ozempic/Wegovy) established the GLP-1 agonist class with ~15-17% average body weight loss.
  • Tirzepatide (Mounjaro/Zepbound) added GIP receptor agonism for ~22% weight loss — significantly better than semaglutide.
  • Retatrutide adds glucagon receptor agonism for up to 24% weight loss in Phase 2, with remarkable liver fat reduction.
  • Research-grade semaglutide is available for investigation, but clinical use requires a prescription for the FDA-approved formulation.
  • The next frontier includes oral formulations, antibody-peptide conjugates, and combinations with muscle-preserving agents.

Current Landscape

The weight loss peptide field has undergone a revolution in the past five years. What started with modest weight loss results from early GLP-1 agonists has evolved into a therapeutic class achieving weight reduction comparable to bariatric surgery — through a weekly injection.

The market is dominated by two pharmaceutical companies: Novo Nordisk (semaglutide) and Eli Lilly (tirzepatide, retatrutide). Their clinical programs have progressively demonstrated that more receptor targets can produce more weight loss, leading to the current multi-agonist era. For a detailed comparison of these compounds, see our GLP-1 receptor agonists deep dive.

Semaglutide

The compound that made the world pay attention. Approved as Ozempic (diabetes, 2017) and Wegovy (weight management, 2021), semaglutide produces 15-17% average total body weight loss at the 2.4mg weekly dose. The SELECT cardiovascular outcomes trial demonstrated a 20% reduction in major cardiac events, independent of weight loss.

Semaglutide remains the most prescribed weight loss peptide globally. Its established safety profile across hundreds of thousands of patients gives physicians confidence that tirzepatide and retatrutide, with less real-world data, can't yet match.

Tirzepatide

Eli Lilly's dual GIP/GLP-1 agonist took the field further with 22.5% average weight loss in the SURMOUNT program. The first head-to-head trial (SURMOUNT-5) showed tirzepatide clearly outperforming semaglutide: 20.2% vs. 13.7% weight loss at 72 weeks.

The GIP receptor component appears to enhance fat oxidation directly in adipose tissue, possibly explaining the additional weight loss beyond what GLP-1 agonism alone achieves. The GI side effect profile is also somewhat better than semaglutide at equivalent weight loss levels.

Retatrutide

The triple agonist (GLP-1 + GIP + glucagon receptor) showed 24.2% weight loss at 48 weeks in Phase 2 — and the curve hadn't plateaued, suggesting even greater weight loss at longer treatment durations. The liver fat data was particularly striking: 86% reduction in liver fat content, far exceeding what semaglutide achieves.

Phase 3 trials are underway. If the results hold, retatrutide could become the most effective pharmacological weight loss agent ever developed.

Emerging Approaches

The pipeline extends beyond incretin agonists:

  • Amgen's MariTide: An antibody-peptide conjugate that activates GLP-1 while blocking GIP. Monthly dosing potential.
  • Orforglipron (Lilly): An oral small-molecule GLP-1 agonist that doesn't require the absorption tricks of oral semaglutide.
  • GLP-1 + anti-myostatin: Combining weight loss with muscle preservation to improve body composition outcomes.
  • Amylin analogs: Cagrilintide (Novo Nordisk) targets a different appetite pathway and is being studied in combination with semaglutide.

The central open question remains: weight regain after discontinuation. Most studies show significant weight return when the drug is stopped, suggesting these may be lifelong medications for many patients.

Further Reading
Deep Dive
GLP-1 Agonists Explained

Detailed receptor-level comparison of semaglutide, tirzepatide, and retatrutide.

 How-To
Managing Side Effects

Dealing with nausea and other GLP-1 effects.

 Industry
Oral Peptides Research

Can oral delivery match injectable efficacy?

References

  1. Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-216. PubMed
  2. Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002. PubMed
  3. Drucker DJ. Mechanisms of action and therapeutic application of glucagon-like peptide-1. Cell Metab. 2018;27(4):740-756. PubMed
  4. Finan B, et al. Retatrutide, a GIP, GLP-1, and glucagon receptor triagonist. N Engl J Med. 2023;389(6):514-526. PubMed
  5. Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity. N Engl J Med. 2023;389(6):514-526. PubMed