What Are GLP-1 Peptides? A Plain-English Guide
GLP-1 peptides like semaglutide and tirzepatide are reshaping weight loss and metabolic health. What they are, how they work, and what to know before starting.
April 28, 2026 · 3 min read · By GLP-FAQ Editors
If you've spent any time on the internet in the last two years, you've heard the names: Ozempic. Wegovy. Mounjaro. Zepbound. They're prescribed for type 2 diabetes and weight loss, and behind every brand sits a class of molecules called GLP-1 receptor agonists — peptides that mimic a hormone your gut already makes.
This guide is the orientation we wish we'd had when we first tried to figure out what these drugs do, who they're for, and why they've become a generational shift in metabolic medicine.
What does "GLP-1" actually mean?
GLP-1 stands for glucagon-like peptide-1, a hormone secreted by your intestines after you eat. Its job is to:
- Tell your pancreas to release insulin (so blood sugar comes down)
- Slow gastric emptying (so food sits longer in your stomach)
- Signal fullness to your brain (so you stop eating)
A GLP-1 receptor agonist is a synthetic peptide that binds to the same receptors as natural GLP-1 — but lasts much longer in your body. Where natural GLP-1 is broken down in minutes, modern peptides like semaglutide can stick around for about a week per dose.
The peptides you'll actually hear about
| Peptide | Brand names | Targets | Notes |
|---|---|---|---|
| Semaglutide | Ozempic, Wegovy, Rybelsus | GLP-1 | The original blockbuster |
| Tirzepatide | Mounjaro, Zepbound | GLP-1 + GIP | Dual-agonist; tends to outperform semaglutide on weight loss |
| Liraglutide | Saxenda, Victoza | GLP-1 | Older, daily injection |
| Retatrutide | (in trials) | GLP-1 + GIP + glucagon | Triple-agonist; promising trial data, not yet FDA-approved |
How they work for weight loss
Three mechanisms compound on each other:
- Reduced appetite. The "food noise" — that low-grade preoccupation with what to eat next — quiets down for most people within the first week.
- Slower digestion. Meals satisfy you for longer because they're physically still in your stomach.
- Better blood sugar control. Stable glucose means fewer insulin spikes, fewer cravings, and a metabolism that prefers fat for fuel.
In trials, semaglutide users lost roughly 15% of body weight over 68 weeks. Tirzepatide users lost up to 22% at the highest dose. For context, that's well past what bariatric surgery achieves for many patients.
What about side effects?
Most are GI: nausea, constipation, occasional vomiting — usually worst in the first week after a dose increase, then fading. Less common but worth knowing about: pancreatitis, gallbladder issues, and (in animal studies, not yet confirmed in humans) thyroid C-cell tumors. This is why titration matters — you start at a sub-therapeutic dose and ramp up over weeks.
Should you consider one?
That's a conversation for you and a clinician — but the candidates who tend to do best are people with:
- BMI ≥ 27 with a comorbidity (high blood pressure, sleep apnea, prediabetes)
- BMI ≥ 30 regardless
- Type 2 diabetes that's not well-controlled on metformin alone
Where to go from here
- How to dose your first month — the titration questions everyone asks
- Reconstitution calculator — for compounded peptide users
- Latest GLP-1 news — trial results, FDA actions, supply updates
The science is moving fast, but the fundamentals haven't changed: GLP-1 peptides work by amplifying a signal your body already sends. Used thoughtfully, with a clinician in the loop, they're one of the most effective metabolic tools we've ever had.
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