Peptide science, explained
Peptides, decoded.
Tirzepatide activates two gut-hormone receptors. Retatrutide activates three. Here's what each one is, how it works, and what the research shows.
2 → 3
receptors targeted: tirzepatide vs retatrutide
39
amino acids in tirzepatide's chain
1×
weekly injection, thanks to a fatty-acid side chain
Important to know
Not a magic fix.
Tirzepatide, retatrutide and other peptides are not magic weight-loss elixirs. They are prescription medicines that support weight loss alongside a healthier lifestyle, never instead of it, and only with a doctor's guidance.
Better food choices
A balanced, reduced-calorie diet: more vegetables, fruit, protein and whole foods; fewer sugary drinks and ultra-processed snacks.
Regular movement
Daily activity you can keep up, building toward about 150 minutes a week, the level used in the weight-loss trials.
A doctor's guidance
A licensed physician decides whether a medicine is right for you, prescribes it, sets the dose and watches for side effects.
Peptides as support
Prescription peptide medicines can help with appetite and blood sugar, making healthy habits easier to keep. They boost the effort, not replace it.
Approved as an add-on
Tirzepatide for weight management is approved for use together with a reduced-calorie diet and increased physical activity.5
Trials included lifestyle change
Everyone in the main weight-loss trials, including the placebo groups, also followed a diet and exercise programme.1
Stopping brings weight back
When people stopped tirzepatide, they regained much of the lost weight. Lasting results depend on lasting habits.16
Never buy or use peptides without a prescription and a doctor's supervision. Prepare for that conversation
Tirzepatide
Two receptors. One weekly peptide.
A dual GIP and GLP-1 receptor agonist, approved in the US as Mounjaro for type 2 diabetes and as Zepbound for weight management and obstructive sleep apnea.
Retatrutide
Three receptors. One weekly peptide.
An investigational triple agonist of the GIP, GLP-1 and glucagon receptors. Phase 3 trials reported in 2026, but it is not approved anywhere yet.
Peptides 101
What is a peptide?
A short chain of amino acids — the same building blocks as proteins, just fewer of them. Many hormones are peptides. Tirzepatide and retatrutide are lab-made peptides modelled on GIP, a hormone the gut releases after you eat.
Each bead is one amino acid. Tirzepatide has 39.
Mechanism
Incretins, explained.
Incretins are gut hormones that prompt the pancreas to release insulin after a meal, mainly when blood sugar is high. Each peptide switches on a different set of hormone receptors.
- GLP-1Insulin, fullness, slower digestion●●
- GIPInsulin, fat-tissue energy handling●●
- GlucagonEnergy use, liver fat burning–●
Tirzepatide · SURMOUNT-1
Up to
20.9%
average weight loss over 72 weeks on the 15 mg dose, versus 3.1% on placebo, in 2,539 adults without diabetes.1
- Placebo3.1
- 5 mg15.0
- 10 mg19.5
- 15 mg20.9
Retatrutide · Phase 2
Up to
24.2%
average weight loss over 48 weeks on the 12 mg dose, versus 2.1% on placebo, in 338 adults without diabetes.6
- Placebo2.1
- 1 mg8.7
- 4 mg17.1
- 8 mg22.8
- 12 mg24.2
Design
Built to last a week.
Natural GIP and GLP-1 last only minutes in the blood. Both peptides carry a fatty-acid side chain that binds albumin, a blood protein, which slows their clearance to a half-life of about 5–6 days.59
Tirzepatide~5-day half-life
Retatrutide~6-day half-life
One segment = one day of the week.
Side effects
Know what to expect.
In trials of both peptides, the most common side effects were digestive. They were mostly mild to moderate and most frequent while the dose was being increased.
- Nausea
- Diarrhea
- Vomiting
- Constipation
- Decreased appetite
- Indigestion
Peptide library
Beyond the headline peptides.
BPC-157, GHK-Cu, cagrilintide, tesamorelin and more, each rated by how strong the evidence really is.
Compare
Which is which?
Receptor targets
Type
Status
Brand names
Development code
Schedule
Headline weight result
Headline HbA1c result
Most common side effects
Developer
These results come from separate trials with different people, doses and durations. They are not a head-to-head comparison.
Safety
Safety comes first.
Both peptides act on powerful hormone systems. Here is what the label and the trials say to watch for.
Common to both
Nausea, diarrhea, vomiting, constipation and reduced appetite — usually mild to moderate, and most likely while the dose is being increased.
Tirzepatide label5
- Thyroid C-cell tumors
- Pancreatitis
- Gallbladder problems
- Low blood sugar
- Kidney problems
- Birth control pills
- Anaesthesia and sedation
Important
Beware of “research peptides.”
Both peptides are sold online as “research chemicals” or “not for human use.” These are not approved medicines: their identity, purity, dose and sterility are unknown. Regulators, including the US FDA, have warned about unapproved and counterfeit versions.15 In 2026 the Philippine FDA issued public health warnings against unregistered “research use” tirzepatide and retatrutide products.13 Retatrutide is not approved anywhere, so any product sold outside a clinical trial is unregulated.
Only use medicines prescribed by a licensed clinician and dispensed by a licensed pharmacy.
News
Latest research updates
Free tools
Know your numbers
Private calculators built on WHO and Asia-Pacific guidance. Nothing you enter leaves your device.
- BMI calculatorCheck your body-mass index on both the WHO and Asia-Pacific scales used in the Philippines.Open
- Waist-to-height ratioA simple check of belly fat: keep your waist to less than half your height.Open
- Protein calculatorHow much protein you need each day to protect muscle, with Filipino food examples.Open
- Eligibility checkA private check of the tirzepatide label and retatrutide trial criteria, with a PDF report for your doctor.Open
Community
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