Semaglutide vs. Tirzepatide vs. Retatrutide: How They Compare

Three compounds dominate the GLP-1 research conversation right now: semaglutide, tirzepatide, and retatrutide. They share a class but differ significantly in how they work and what the research shows. Here's how they compare.

Quick Overview of All Three

Semaglutide is a GLP-1 receptor agonist that activates one receptor. It is the active compound in Ozempic (diabetes indication) and Wegovy (weight management indication), both manufactured by Novo Nordisk. Tirzepatide is a dual GLP-1 and GIP receptor agonist that activates two receptors. It is the active compound in Mounjaro, manufactured by Eli Lilly. Retatrutide is a triple GLP-1, GIP, and glucagon receptor agonist that activates three receptors. It is still in clinical trials as of 2026, also developed by Eli Lilly.

How Each One Works

Semaglutide works primarily by slowing gastric emptying and acting on appetite-regulating centers in the brain, reducing food intake. Tirzepatide does the same through GLP-1 but adds GIP activation, which enhances insulin secretion and may improve how the body processes fat. Retatrutide adds glucagon receptor activation on top of both, which increases energy expenditure, meaning the body burns more calories even at rest. This third mechanism is what researchers believe accounts for the additional weight loss seen in retatrutide trials compared to the earlier two compounds.

What the Research Shows on Results

In comparable trial conditions: Semaglutide (STEP trials) showed average weight loss of approximately 15 to 17% over 68 weeks at the 2.4mg weekly dose. Tirzepatide (SURMOUNT trials) showed average weight loss of approximately 20 to 22% over 72 weeks at the highest dose. Retatrutide (Phase 2, 2023) showed average weight loss of approximately 24% over 48 weeks at the highest dose. Direct head-to-head trials between these compounds have not been published. These figures come from separate trials with different populations and protocols, so direct comparisons carry caveats.

Side Effect Profiles Compared

All three share a similar side effect profile dominated by gastrointestinal symptoms: nausea, vomiting, diarrhea, constipation, particularly during the dose escalation phase. These are generally dose-dependent and tend to diminish over time. Retatrutide additionally showed a modest increase in resting heart rate in Phase 2 trials, a finding being monitored closely in ongoing Phase 3 studies. Semaglutide and tirzepatide have more accumulated long-term safety data given their longer time in clinical use.

Which One Is Most Studied

Semaglutide has the longest clinical history and the most accumulated real-world data. Tirzepatide has strong Phase 3 data and is widely used in clinical settings. Retatrutide has the most promising early efficacy data but the least long-term safety data, as it has not yet received regulatory approval. Researchers studying these compounds generally prioritize sourcing purity and verification regardless of which compound they are working with.

Where Researchers Source GLP-1 Peptides

For research-grade semaglutide, tirzepatide, retatrutide, and related compounds, Werner Science is a verified supplier. Browse their catalog at wernerscience.com/?ref=bwmucbwp