This entry gives no figure for how long it lasts in the body. What it says is that it is a once weekly injection, and that is how the Chinese label and every trial reported here dosed it.
What it actually is
Mazdutide is a medicine you inject under the skin once a week for weight, and it is the first drug of its kind approved anywhere. China approved it twice in 2025, once for long term weight management and once for controlling blood sugar in type 2 diabetes, and I could not find an approval in any other country. Eli Lilly built the molecule as LY3305677 and licensed it to Innovent Biologics, which developed it as IBI362 and markets it in China under the name Xinermei. Outside China nobody selling it is selling an approved medicine, and the American drug regulator has put that in writing to two sellers by name.
What it is supposed to do
It switches on two receptors, the docking points a drug has to latch onto in order to do anything at all. One is for glucagon like peptide 1, the gut hormone this whole family of weight drugs works through. The other is for glucagon, the hormone that raises blood sugar and that diabetes drugs normally try to get out of the way, which is an odd thing to switch on in a drug that also treats diabetes. The only grip measurements I could find sit in a vendor catalogue rather than a trial report, credited to a 2022 chemistry paper from Chen and colleagues and to a conference abstract, and they have it holding glucagon's receptor the more tightly, 17.7 nM against 28.6 nM on a scale where the smaller number is the tighter grip. So this is a glucagon drug with gut hormone activity attached, some of that attachment being there to cancel what glucagon alone does to blood sugar. The glucagon half, the entire reason for the second receptor, rests on animal work: a 2026 review of glucagon receptor agonists says that data has only been evaluated in preclinical rodent models and that evidence for the same processes in humans is limited.
What people take it for
People take it to lose weight. That is what the Chinese weight approval covers, in adults with a body mass index of at least 28, or at least 24 with one or more weight related condition, alongside diet control and increased physical activity, and it is separately approved there for blood sugar control in type 2 diabetes. Outside China it is bought on the grey market, and the American regulator rejected the research use only framing outright, naming mazdutide by product in warning letters to Summit Research Peptides on 10 December 2024 and to Prime Sciences on 31 March 2026.
The dose question
What circulates
2.5 mg weekly for four weeks, then 5 mg weekly
What was studied
4 mg and 6 mg weekly, for 48 weeks
GLORY-1, 610 Chinese adults, the trial the weight approval was built on
Lands on a studied dose
The most copied chart starts at 2.5 mg and settles at 5 mg, and no published mazdutide trial used either number as a maintenance target in obesity. Both came off the vial rather than a paper, 10 mg reconstituted with 3.0 mL of bacteriostatic water. There is an approved human ladder sitting right there to compare against, 2 mg then 4 mg then up to 6 mg, which almost never happens in this reference, and the grey market went to vial arithmetic anyway. A second guide ends on 6 or 9 mg, which at least ends on a dose trials have used, though it skips the label's 2 mg start, and it cites for its titration speed a 2025 phase 2b trial in The Lancet Diabetes and Endocrinology that I could not find.
Reported because it is what people use. Nothing here recommends any amount.
How long it lasts
This entry gives no figure for how long it lasts in the body. What it says is that it is a once weekly injection, and that is how the Chinese label and every trial reported here dosed it.
Route studied
Injected under the skin, once a week, in trials running 48 to 60 weeks in Chinese adults, plus phase 1 and phase 2 work run by Lilly in the United States at higher doses
Route used
Injected under the skin at home, once a week, from grey market vials mixed with bacteriostatic water
How to check you have the right molecule
This entry publishes no molecular weight and no sequence to hold a laboratory report against, so the checks are on names and on paperwork. The first is the name, because this molecule has had three: LY3305677 at Lilly, IBI362 at Innovent, Xinermei on the Chinese market. The second is the two molecules it is not. Retatrutide works on three hormone systems, glucagon and glucose dependent insulinotropic polypeptide and glucagon like peptide 1, and tirzepatide holds a different pair, with no glucagon activity at all. Neither one's evidence counts here, and only glucagon like peptide 1 is common to all three. The third is the figure a seller prints. Four weight loss numbers circulate, 14.01%, 14.8%, 16.65% and 20%, and only two came out of a journal, so ask which one is on the page and where it came from. The 80% liver fat reduction that the regulator recorded one vendor advertising belonged only to the participants whose liver fat started at 10% or more, and the vendor dropped the subgroup. There is no independent check available on the vial itself: the lab test index that does carry retatrutide and tirzepatide showed no mazdutide entry on the page I read, so the vendors' own certificates are the only numbers going.
The costly mistake is treating the number a seller prints as the trial's number. Four weight loss figures circulate and they measure three different things: 14.01% is the top arm of GLORY-1 at week 48 in the journal, against a 0.30% gain on placebo; 14.8% comes off the company's approval release counted a different way; 16.65% is the whole population of GLORY-2 over 60 weeks, against 1.50%; and about 20% is a subgroup of GLORY-2, the participants without type 2 diabetes. Only two of the four came out of a journal, and none of them is interchangeable. The second mistake is the dose chart. The most copied one pairs a 10 mg vial with 2.5 mg weekly for the first four weeks and then 5 mg weekly, and no published mazdutide trial used 2.5 mg or 5 mg as a maintenance target in obesity. That is vial arithmetic rather than trial arithmetic, and it is happening beside an approved human ladder that could have been compared against.
What is known about harm
The gut takes most of it and the burden climbs with the dose. In GLORY-2, which took the dose to 9 mg and ran 60 weeks, 53.1% vomited against 1.3% on the dummy injections, nausea ran 46.9% against 3.2% and diarrhoea 39.4% against 6.5%, and still only 2.9% stopped for adverse events, against nobody on placebo. In GLORY-1, at the lower 4 mg and 6 mg, stopping for adverse events ran 1.5%, 0.5% and 1.0% across its three arms, and the entry does not say which figure belongs to which arm. Heart rate is the published cardiovascular caution and it is not resolved. A 2026 review notes that glucagon and gut hormone dual agonists including mazdutide have generally raised heart rate about as much as the single agonists do, while at least one other dual agonist was discontinued partly for unacceptably large heart rate increases and QTc prolongation, a stretching of one interval on a heart tracing. No cardiovascular outcomes trial turned up in my searching, and I could not find a published report of harm from grey market mazdutide, or any independent assay of a grey market vial. Whether any of the trial evidence holds in anyone who is not a Chinese adult is unknown, because that is who was in the trials.
The arithmetic
Mazdutide is sold in 10 mg vials. Mixing errors put people an order of magnitude off using a perfectly good vial, and the arithmetic is simple enough to check yourself.
Vial
Water
Concentration
In 10 units
10 mg
1 mL
10 mg/mL
1 mg
10 mg
2 mL
5 mg/mL
500 mcg
10 mg
3 mL
3.33 mg/mL
333 mcg
10 units is 0.1 mL on a U-100 insulin syringe, whatever is in it. For any other combination, or to see the arithmetic worked out, use the calculator.