Why one category holds very different things
"Weight loss peptide" is a shopping category, not a pharmacological one. The label is applied to regulator-approved prescription medicines with tens of thousands of participants behind them, and in the same breath to research chemicals whose entire human record is a handful of volunteers or nothing at all. Grouping them together makes the second kind look like the first.
The useful split is by mechanism. One group acts on the incretin system — the gut hormone signalling that governs insulin release, gastric emptying and satiety. Another group acts on fat metabolism or mitochondrial signalling, a mechanistically distinct target with a far thinner evidence base. Knowing which group a compound belongs to tells you more than any before-and-after photograph.
The incretin pathway in plain terms
After a meal, the small intestine releases hormones called incretins. Two matter here: GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide). They prompt the pancreas to release insulin in proportion to what has actually been eaten, slow the rate at which the stomach empties, and signal satiety to the brain. Natural GLP-1 is broken down within a couple of minutes.
Incretin drugs are engineered analogues of those signals, modified to resist that breakdown so a single administration lasts days rather than minutes. They are not stimulants, they are not thermogenics, and they do not act directly on fat tissue. They occupy a receptor the body already uses and hold the signal open for longer.
The differences between the incretin compounds come down to how many receptors each one engages. Semaglutide engages GLP-1. Tirzepatide engages GLP-1 and GIP. Retatrutide engages GLP-1, GIP and the glucagon receptor. More receptors is not automatically better; it means a wider range of effects, both intended and not, and in retatrutide's case a much shorter safety record.
The compounds, and where each one stands
Each entry links to a full profile page with mechanism, half-life, evidence grade, side-effect profile and study references.
- Semaglutide
GLP-1 receptor agonist. Approved for chronic weight management under several brand names; the largest human evidence base of any compound on this page.
- Tirzepatide
Dual GIP and GLP-1 receptor agonist. Approved products exist; the second receptor is the main structural difference from semaglutide.
- Retatrutide
Triple agonist at GIP, GLP-1 and glucagon receptors. Investigational — phase 2 data are published, but it is not an approved medicine anywhere.
- AOD-9604
A fragment of human growth hormone studied for effects on fat metabolism. Human trials did not separate it from placebo on body weight.
- MOTS-c
A mitochondrial-derived peptide studied for AMPK signalling and metabolic markers. Evidence is preclinical and early.
- 5-Amino-1MQ
A small-molecule NNMT inhibitor, not a peptide, frequently grouped with them in the same marketing. Animal data only.
Reading the evidence grades
Every profile on this site carries an evidence grade, and in this category the grades are unusually spread out. Strong means multiple randomised, placebo- controlled human trials plus regulatory review — semaglutide and tirzepatide sit here. Moderate means real human data at a smaller scale. Emerging means convincing preclinical work with human studies only beginning. Limited means animal or in-vitro work, or old human studies nobody has replicated.
A grade describes the quality of the record, not the size of an effect. AOD-9604 is a clean example: the human trials were run, they were reasonably designed, and the compound did not separate from placebo. That is informative evidence of absence, and it is still being sold.
The safety and evidence guide works through how to interrogate a claim: was it in humans, was it randomised and controlled, and has anyone reproduced it.
Approved medicine versus research chemical
This distinction is legal and practical rather than chemical. An approved product has a licensed manufacturer, a verified concentration, a printed label, an established sterility standard and a regulator that can recall it. A vial sold "for research purposes only" has none of those guarantees: purity, identity, sterility and the actual quantity inside are unverified, and a certificate of analysis describes one batch at one moment and can be fabricated outright.
An investigational compound such as retatrutide is a further step removed. Published phase 2 results describe what happened under trial conditions with monitored participants, screening criteria and a known drug supply. None of those conditions apply to material bought online.
Where the calculators fit
The most common confusion in this category is not biological, it is arithmetic. Milligrams, millilitres and syringe units are three different measurements, and the relationship between them changes with every reconstitution. Ten units on an insulin barrel is a volume, not a quantity of peptide — how much peptide it holds depends entirely on how much diluent went into the vial.
The calculators below perform that conversion and show every formula, so the arithmetic can be checked on paper. They are unit converters. They contain no dosing tables, suggest no titration schedule and make no recommendation for any person.
The storage and reconstitution guide covers why lyophilised powder is stable while solution is not, and how concentration is derived in the first place.
Things this page deliberately does not say
- Which compound is best. That depends on a medical history this site cannot see.
- How much anyone should take, or how to titrate. That belongs to a prescriber working from an approved label.
- How much weight anyone will lose. Trial averages describe populations, not people.
- Where to buy anything. This site lists no vendors and takes no affiliate revenue.
Incretin compounds are prescription medicines in most jurisdictions, and the ones that are not approved are not approved for a reason. Anyone considering them should be talking to a clinician who can review their history, their other medications — GLP-1 agonists slow gastric emptying and therefore change how other drugs are absorbed — and whether the approach is appropriate at all. See the full disclaimer.