Semaglutide, Tirzepatide and Retatrutide Compared

In the past few years, a class of peptide-based compounds has fundamentally changed what is possible in weight management. The results being reported, both in clinical trials and by real people, are unlike anything the industry has seen before.

At the centre of this shift are three compounds: Semaglutide, Tirzepatide and Retatrutide. You may have heard their brand names, Ozempic, Wegovy and Mounjaro, mentioned in the media or by people in your network. But understanding what these compounds actually are, how they differ from each other and what the evidence says requires a closer look.

This article breaks down each compound, compares the mechanisms, and helps you think through which might be the most relevant for your situation.

A Quick Primer: What Are GLP-1 Receptor Agonists?

Before comparing the three compounds, it helps to understand the shared mechanism that underpins all of them.

GLP-1 stands for Glucagon-Like Peptide-1. It is a hormone your body naturally produces in the gut in response to eating. Its main jobs are to:

• Signal the pancreas to release insulin in response to blood glucose
• Suppress glucagon (a hormone that raises blood sugar)
• Slow the rate at which the stomach empties food into the intestine
• Send satiety signals to the brain, reducing hunger

In people without metabolic dysfunction, this system works well. But for many people, particularly those dealing with obesity or insulin resistance, the GLP-1 signal is blunted or the body does not respond to it effectively.

GLP-1 receptor agonists are compounds that mimic or amplify this signal, essentially turning the volume up on a mechanism the body already uses to regulate appetite and metabolism.

Semaglutide, Tirzepatide and Retatrutide all work through GLP-1 pathways, but they differ in important ways.

Semaglutide: The Established Standard

Semaglutide is a GLP-1 receptor agonist developed by Novo Nordisk. It was first approved for type 2 diabetes management (as Ozempic) and later approved at a higher dose specifically for weight management (as Wegovy).

How it works:
Semaglutide binds to and activates GLP-1 receptors throughout the body, mimicking the natural GLP-1 hormone but with a significantly longer half-life. Where natural GLP-1 is broken down within minutes, Semaglutide remains active for approximately seven days, making once-weekly dosing possible.

What the evidence shows:
The STEP clinical trial programme is the most comprehensive dataset we have. In STEP 1, participants on 2.4mg weekly Semaglutide lost an average of 14.9% of their body weight over 68 weeks, compared to 2.4% in the placebo group. These are meaningful numbers. For context, most conventional weight loss medications had previously achieved 5 to 8% weight loss in comparable trials.

Who it tends to suit:
Semaglutide is the most established of the three. The long-term safety data is the most mature, and the clinical experience is the broadest. For someone new to this category of compounds, it is often the starting point.

Common side effects:
Nausea is the most frequently reported side effect, particularly in the early weeks as the dose is titrated up. Other gastrointestinal effects including constipation, diarrhoea and reduced appetite are also commonly reported. These typically improve as the body adjusts.

Tirzepatide: The Dual Agonist

Tirzepatide, developed by Eli Lilly, represents a meaningful step forward in this class. Where Semaglutide targets only GLP-1 receptors, Tirzepatide is a dual agonist, meaning it activates both GLP-1 receptors and GIP receptors simultaneously.

What is GIP?
GIP stands for Glucose-dependent Insulinotropic Polypeptide. Like GLP-1, it is an incretin hormone produced in the gut after eating. GIP influences insulin secretion and, importantly, has receptors in fat tissue that affect how the body stores and metabolises fat.

The theory behind dual agonism is that activating two complementary pathways produces a more pronounced effect on appetite, insulin sensitivity and fat metabolism than activating either pathway alone.

What the evidence shows:
The SURMOUNT trial programme validated this approach. In SURMOUNT-1, participants on the highest dose of Tirzepatide (15mg weekly) lost an average of 20.9% of their body weight over 72 weeks. At the time of publication, these were the most significant weight loss outcomes ever recorded in a pharmaceutical trial for a non-surgical intervention.

Who it tends to suit:
People who have used Semaglutide and found the response plateaued, or those who want a more aggressive intervention from the outset, are often drawn to Tirzepatide. The greater efficacy comes with a similar side effect profile to Semaglutide, though some studies suggest slightly higher rates of gastrointestinal side effects, particularly at higher doses.

Retatrutide: The Triple Agonist

Retatrutide is the newest of the three and the most powerful in terms of receptor engagement. Where Tirzepatide activates two pathways, Retatrutide is a triple agonist, targeting GLP-1, GIP and glucagon receptors simultaneously.

The role of glucagon:
Glucagon is primarily known as a hormone that raises blood sugar by signalling the liver to release stored glucose. It might seem counterintuitive to activate a glucagon pathway in a metabolic context, but glucagon also significantly increases energy expenditure. By adding glucagon receptor activation to the GLP-1 and GIP mechanisms, Retatrutide aims to not only reduce caloric intake but also increase the rate at which the body burns energy.

What the evidence shows:
Retatrutide is at an earlier stage of its clinical development than Semaglutide or Tirzepatide, but the Phase 2 data published in 2023 was remarkable. Participants on the highest dose (12mg weekly) lost an average of 24.2% of their body weight over 48 weeks, with many researchers noting the trajectory had not yet plateaued at the end of the trial.

Who it tends to suit:
Retatrutide is currently the most potent option in this class by the numbers. It is also the least mature in terms of long-term safety data. People who are well-informed about the risk profile and are looking for the most aggressive metabolic intervention currently available are those most likely to consider it.

As Phase 3 trials continue, the picture will become clearer. For now, it is a compound to watch closely.

Comparing the Three: A Quick Reference

Which One Should You Consider?

There is no single answer that applies to everyone. Some factors worth thinking through:

Experience with the category: If you are new to GLP-1 peptides, starting with Semaglutide allows you to understand how your body responds to this class before moving to more potent options.

Degree of metabolic challenge: Someone with significant obesity and metabolic complications may benefit from the added potency of Tirzepatide or Retatrutide.

Risk tolerance: Greater potency often comes with less long-term safety data. Semaglutide has the longest track record. Retatrutide is the most novel.

Your broader protocol: These compounds work best alongside lifestyle changes, not as a substitute for them. How you approach nutrition, activity and sleep will significantly influence outcomes.

If you want to talk through your specific situation, our team is available on WhatsApp and can help you think through the options without pressure.

Disclaimer: The information in this article is for educational purposes only. STRIATA peptides are research compounds and are not approved medicines. Always consult a qualified healthcare professional before beginning any weight management protocol.