Approved, with a cloned trial record on the registry
What it actually is
Tirzepatide is a medicine you inject under the skin once a week. It is approved and sold under two brand names, Mounjaro for type 2 diabetes and Zepbound for weight and for a breathing problem that interrupts sleep. Unlike almost everything else in this reference, it has been tested in very large trials against dummy injections, and on the highest dose in the biggest weight trial people lost about a fifth of their body weight over 72 weeks.
What it is supposed to do
It is a lab-made copy of one of the hormones the gut releases around a meal, changed so that it switches on two hormone docking points at once instead of one. A fatty tail attached to the molecule makes it linger in the body long enough for a single injection to cover a week. In the trials, that produced lower blood sugar and lower body weight, and those two effects did not shrink together at the bottom of the dose range: the smallest dose ever carried through a randomised trial held more than half of the blood sugar effect while giving only 0.9 kg of weight loss in six months.
What people take it for
People take it to lose weight and to control type 2 diabetes, and it is also approved for moderate to severe sleep apnoea in people with obesity. Online, a widespread practice is taking far smaller weekly amounts than the label uses, roughly 0.25 to 1.5 mg, marketed as microdosing. Those smaller amounts appear on vendor and telehealth pages, not in the trial record.
The dose question
What circulates
Microdoses below 2.5 mg weekly
What was studied
5, 10 and 15 mg weekly
SURMOUNT-1, about a fifth of body weight at the top dose
Microdosing was tested once. At the smallest dose people lost under a kilogram in six months.
Reported because it is what people use. Nothing here recommends any amount.
How long it lasts
The entry gives no number for how long it lasts in the body. It says only that a fatty tail on the molecule stretches its stay far enough for one injection a week under the skin, which is how every human trial dosed it.
Route studied
Under the skin, once a week, in large trials
Route used
Under the skin at home, once a week. Pharmacy mixed versions have also been sold as under the tongue liquids and dissolving tablets, neither an approved way to take it.
How to check you have the right molecule
This entry publishes no purity or mass figure to compare against, so the check that matters is on paperwork, and it has exact strings. If a seller or clinic points you at trial record NCT07481747, that record is a copy of the real SURMOUNT-1 trial, word for word in its title, listing 2,539 participants, which is the number the real finished trial ended with, under sponsor Hudson Biotech at a single hospital in Shenzhen. The field that settles it is the file number: the copy reads I8F-MC-GPHK(b), while Eli Lilly's genuine file number is I8F-MC-GPHK with no letter on the end, and searching that string returns exactly two records where there should be one. On a pharmacy mixed vial, added vitamin B12 is the other flag, because in ten samples tested tirzepatide reacted with it to form an impurity nobody had identified before.
The mistake that costs money and safety is quoting the trial numbers while buying something the trials never used. The 20.9% figure comes from branded tirzepatide at the top weekly dose over 72 weeks, whereas the only randomised weight result anywhere near the tiny doses sold online was under a kilogram in six months, and roughly a quarter of people on that dose still had stomach and gut side effects.
What is known about harm
Stomach and gut side effects were common and climbed with the dose: about 23 in 100 people at the smallest dose tested, about 51 in 100 in the middle and about 66 in 100 at the largest, against about 10 in 100 on dummy injections. Both brands carry the strongest kind of warning label for thyroid tumours, which were seen in rats and whose meaning for people is undetermined, and both are ruled out for anyone with a personal or family history of a rare thyroid cancer called medullary thyroid carcinoma or the inherited condition MEN 2. In the trial where people were switched off it, much of the weight came back, and what the newly found impurity in pharmacy mixed vials does to a person is unknown, which the paper that found it states outright.
Everything on this page is a summary. The citations, the studies and the reasoning live in the full entry.