What is it?
What it is: an Eli Lilly medicine for type 2 diabetes and obesity — a 39-amino-acid peptide that acts on two hormone receptors at once, GIP and GLP-1. It is called a “dual agonist”, sometimes a “twincretin”.
Status: a prescription medicine in the USA, the EU, the UK and many other countries (Mounjaro, Zepbound).[1][8]
When it appeared: developed at Lilly in the mid-2010s; first paper in 2018; first approval by the FDA on 13 May 2022.[13]
Sport: not on WADA’s 2026 Prohibited List, but included in the Monitoring Program — anti-doping laboratories track how often athletes use it.[12]
After a meal, the gut releases hormones called incretins: they help the pancreas release insulin when blood sugar rises and tell the brain that a person is full. Tirzepatide mimics two of them:
- GLP-1 reduces appetite, slows stomach emptying and boosts insulin release after meals. This is how semaglutide (Ozempic, Wegovy) works.
- GIP also boosts insulin release and, according to current data, affects fat tissue and appetite centres.
| Drug | Receptors | Status |
|---|---|---|
| Semaglutide | GLP-1 | approved |
| Tirzepatide | GIP + GLP-1 | approved |
| Retatrutide | GIP + GLP-1 + glucagon | under investigation, not approved |
Tirzepatide is a single molecule, not a mixture of two drugs. And “dual” does not mean “50/50”: it “sticks” to the GIP receptor about as well as the natural hormone, but acts on GLP-1 more weakly and slightly differently.[14] Scientists have not fully explained why adding GIP strengthens the effect: for a long time it was thought that in obesity GIP should rather be blocked. Tirzepatide became an argument for stimulating it, but the debate continues.
For those who want more detail: the structure of the molecule
Development code: LY3298176. A peptide based on the GIP sequence: positions 2 and 13 hold non-standard amino acids (Aib) that protect the chain from enzymes; a fatty acid (C20 diacid) is attached via a linker to the lysine at position 20, binding the molecule to blood albumin, so the drug lasts about a week. Formula C₂₂₅H₃₄₈N₄₈O₆₈, mass ≈ 4813 g/mol; CAS 2023788-19-2; UNII OYN3CCI6QE; DrugBank DB15171; ATC A10BX16.[7][1]
When did it appear?
Patents and copies
Lilly’s main US patent on the molecule runs until January 2036; additional patents (formulation, the pen, methods of use) may extend protection to roughly 2039–2041. In 2026 the FDA accepted Sandoz’s applications for a copy of tirzepatide, but there are no approved copies in the USA or EU yet.[29] For scale: Mounjaro and Zepbound earned Lilly 36.5 billion dollars in 2025 — tirzepatide became the world’s best-selling drug.[31]
What is it used for?
Official indications
| Indication | USA (FDA) | EU (EMA) |
|---|---|---|
| Type 2 diabetes in adults | ✅ Mounjaro, 2022 | ✅ Mounjaro, 2022 |
| Type 2 diabetes in children aged 10+ | ✅ 2025 | ✅ |
| Obesity, and overweight with related conditions | ✅ Zepbound, 2023 | ✅ Mounjaro, 2023 |
| Sleep apnoea with obesity | ✅ Zepbound, 2024 | — |
| Reducing the risk of heart attack, stroke and cardiovascular death in type 2 diabetes | ✅ Mounjaro, 2026 | no separate indication granted; data added to the product information |
| Heart failure with preserved ejection fraction in obesity | — | no separate indication granted; data added to the product information |
Regulators assess the same data differently. On heart failure, the EMA concluded that it was unclear whether there was any benefit beyond weight loss, and that treating obesity in these patients is already covered by the indications.[9] On cardiovascular risk, the FDA approved the indication and the EMA did not.[8]
In Russia the original Lilly product is not sold. In 2022, after the start of the war in Ukraine, Lilly suspended operations in Russia, then left the market, and in November 2024 it terminated its own Eurasian patent on tirzepatide.[27][32] After that, Russian pharmaceutical companies registered their own tirzepatide products (for example, “Tirzetta” and “Sejaro”); they are prescription-only.[33] Data from Lilly’s trials apply to Lilly’s product; the Russian products have their own registration data.
Under investigation (not yet indications): heart protection in people with obesity without diabetes (SURMOUNT-MMO, about 15,000 participants, ongoing), fatty liver disease, kidney disease, obesity in adolescents.
Unofficially: weight loss without a medical indication, “cutting” in bodybuilding, and “microdosing” — doses below those studied, to make a calorie deficit easier to maintain. There are no scientific data on “microdosing”.
The different kinds of “tirzepatide”
| Lilly original | Compounded “copies” in the USA | “Research” vials (e.g. ZPHC) | |
|---|---|---|---|
| Approval | yes: FDA, EMA, etc. | no; permitted during the shortage, now only in narrow cases | no |
| What has been studied | thousands of people in trials | the product itself has not been studied | the product itself has not been studied |
| Who checks quality | regulators | the pharmacy’s licence; the FDA has found sterility violations | only the manufacturer — a matter of trusting it |
| Additives | none | often B12, niacinamide — such combinations have not been studied | as labelled |
| Doctor | required (prescription) | on prescription, often online | none |
The FDA’s position: the only approved tirzepatide products in the USA are Mounjaro and Zepbound.[5] The regulator does not regard a “research use only” label as a defence if the product is in effect sold to people; in 2026 the FDA sent warnings to telehealth services and pharmacies selling tirzepatide “copies”.[34][35]
If there is an approved drug, why buy vials?
The main reasons are price (in the USA about a thousand dollars a month without insurance, and insurance often does not cover obesity treatment) and the prescription: people without an indication, for example those who want it “for definition”, will not be prescribed it. A vial wins on price and availability but loses on the main point: what is inside has to be taken on trust, and there is no medical supervision.
What people expect from it and why it is popular
| Expectation | Where it comes from | What the data say |
|---|---|---|
| Lose 15–20% of body weight | Lilly’s trials, media | on average ~20% over 72 weeks — while the drug is being taken |
| “Stronger than Ozempic” | head-to-head comparison, social media | in a head-to-head trial weight loss was greater than on semaglutide; this is one trial with specific conditions |
| “Quiet in the head” | patients, social media | many describe it this way, but it is not a measured trial outcome |
| Lose weight once and for all | expectation of a “course” | not supported: after stopping, most of the weight usually comes back |
| Protect the heart | 2026 FDA approval | shown in diabetes with heart disease; in obesity without diabetes a trial is ongoing |
| “Burn fat while keeping muscle” | fitness bloggers | both fat and lean mass are lost |
Its popularity rests on the largest weight-loss figures among approved drugs, one injection a week and a constant presence in the news. The 2022–2024 shortage and the high price created a huge market for “copies” and “research” vials.
What has research shown?
All the trials below were sponsored by Lilly. The figures apply to the original product.
Main results
- Weight loss. In the main obesity trial (2,539 people, 72 weeks), weight fell by an average of 15–21% depending on the dose vs 3% on placebo.[15]
- Comparison with semaglutide (751 people): −20.2% body weight vs −13.7% over 72 weeks. The trial was open-label and funded by Lilly.[17]
- What happens after stopping. After 36 weeks of treatment, some participants were switched to placebo under blinded conditions: over the following year they regained an average of 14% of their weight, while those who continued lost another 5.5%. 89.5% of those who continued maintained at least 80% of the weight lost, compared with only 16.6% of those who stopped.[16] Tirzepatide is not a “course” but long-term treatment.
- What the lost weight consists of. About 75% fat and about 25% lean mass — the same proportions as in people losing weight by diet alone. Lean mass is not only muscle but also water, organs and connective tissue.[18]
- The heart. In SURPASS-CVOT, tirzepatide was compared with dulaglutide, which already has proven heart protection: heart attack, stroke or cardiovascular death occurred in 12.2% vs 13.1%. Tirzepatide proved non-inferior, but it could not be shown to be superior.[19] An additional analysis of a broader set of outcomes showed a 16% risk reduction, but such analyses are less reliable.[20]
- Heart failure (731 people with obesity): worsening or cardiovascular death in 9.9% vs 15.3% on placebo; the number of events was small (92).[21]
What the trials have not yet shown
- heart protection in people with obesity without diabetes (SURMOUNT-MMO is ongoing);
- safety over decades;
- safety in pregnancy and breastfeeding;
- anything at all about “research” vials and compounded “copies”: they have not been studied.
What people who have used it say
Personal experience is not proof. On Reddit almost all the authors say they received the original product prescribed by a doctor; on YouTube it is more often compounded “copies”, or they do not say. Videos were chosen at random (except obviously promotional ones). Doses, regimens and personal details are not given.
More than two years, minus ~63 kg: weight has been maintained for 8 months already. The worst part — a few episodes of nausea and vomiting in the first year, less and less over time. Never once wanted to quit.[37]
Three weeks, a man who trains hard: “food is no longer in my head”, minus ~6 kg. Honestly lists the downsides — bouts of nausea, weakness in the gym, dizziness, difficulty drinking enough water; attributes some of it to a sharp calorie deficit. Does not say which product he took.[44]
Side effects with every dose increase: flu-like feeling, aches, injection-site reactions, constipation. On a lower dose weight did not fall; on a higher one it does, but the side effects return. The author is deciding what to do together with a doctor.[38]
A successful discontinuation: minus 30 kg, then gradual tapering; over several months plus ~3 kg; the “food noise” came back, but it is manageable.[39]
A compounded “copy” after the original: the first week almost without side effects, fewer thoughts about food. The author notes that the reaction may differ on another version of the drug.[45]
Stopped because of abdominal pain: minus ~25 kg, then increasing pain with vomiting after injections. The doctor suspected pancreatitis — tests did not confirm it. After stopping the pain went away, but the “food noise” returned, along with a difficult emotional state driven by fear of regaining weight.[40]
Rapid regain after stopping: minus ~20 kg, and ~11 kg came back within 7 weeks of stopping; the “food noise”, the author says, is stronger than before treatment.[41] Similar stories: plus 7–8 kg after stopping because of the price[42] and a gradual gain of ~10 kg over 3 years despite regular running.[43]
A compounded “copy” with vitamin B12, ~90 days: insomnia on injection day, very vivid dreams, reduced libido. The author does not know whether tirzepatide or B12 is to blame (more in “Possible risks”).[46]
What specialists say in videos
Personal opinions, not recommendations.
Says frankly that no trial has studied people like him — lean and without diabetes — and calls it a personal “bet”, not advice. Carefully analyses SURPASS-CVOT: no superiority on the primary endpoint. Chose tirzepatide over retatrutide because of the smaller increase in heart rate. His “food noise” disappeared; in the first weeks — nausea and fatigue.
Minus ~3 kg in a month; the main downside is constipation, plus a loss of strength in the gym. Unexpectedly, his nicotine cravings disappeared. He calls buying vials labelled “not for human consumption” dangerous: in his words, there is no way to know whether the product is sterile or whether the dose is too high or too low.
The most common plus is that constant thoughts about food disappear. The most common minuses are nausea at the start and with dose increases, constipation and fatigue. The main topic on Reddit is stopping: in three of five stories, weight partly returned after stopping (from 7–8 to ~11 kg), and one author managed to keep the result. This matches the trials: after stopping, part of the lost weight usually returns, but not all of it. There are no reviews of ZPHC vials in this selection.
Possible effects
Possible risks
From the official prescribing information
- Stomach and gut — the most common: in SURMOUNT-1, nausea in 27.5%, diarrhoea in 20.9%, constipation in 13.6%, vomiting in 10.8%, more often during dose increases.[22]
- Thyroid tumours in rats; whether tirzepatide causes them in humans is unknown. In the US prescribing information this is a boxed warning — the strictest form.[2]
- Pancreatitis. In January 2026 the MHRA strengthened warnings for the whole class: 1,296 reports of pancreatitis since 2007, 19 of them fatal. The risk is small, but if it is suspected, treatment must be stopped immediately.[10]
- Gallbladder, dehydration and kidneys, low blood sugar in combination with insulin, diabetic retinopathy, aspiration under anaesthesia, reduced reliability of contraceptive pills, allergy.
What regulators reviewed and dropped
- Suicidal thoughts. In January 2026 the FDA analysed 91 trials of the class (about 108,000 participants), found no increased risk and requested removal of the warning, including from the Zepbound prescribing information.[6]
- Optic nerve damage (NAION). The 2026 UK warning concerns semaglutide; no link has been established for tirzepatide.
The original and unapproved versions: what their side effects have in common
Unapproved versions are compounded “copies” and “research” vials. These products themselves have not been studied, so below is a comparison of what is known about the original with what regulators, Lilly and users report.
| Effect | Original | Unapproved versions | What they share |
|---|---|---|---|
| Nausea, vomiting, diarrhoea, constipation | the most common | the same complaints; the FDA notes that many reactions resemble those to the original[5] | shared — an effect of the molecule |
| Pancreatitis, gallbladder, dehydration | rare, listed in the prescribing information | no separate statistics | shared — expected whenever the product actually contains tirzepatide |
| Serious reactions, hospitalisations | rare | more than 730 reports to the FDA; some are dosing errors[5] | shared in nature, higher risk: the dose is not controlled |
| Injection-site reactions | usually mild | plus a risk of infection: Lilly found bacteria, the FDA found sterility violations[25] | partly; contamination only in unapproved versions |
| Impurities, a different substance, wrong dose | ruled out by manufacturing controls | impurities, an altered structure, in one case only a sugar alcohol (according to Lilly)[25] | only in unapproved versions |
| Additives (B12, etc.) | no additives | in 2026 Lilly found an impurity of unknown toxicity in all 10 samples of “tirzepatide with B12”[26] | only in unapproved versions |
| Unusual complaints from social media | not among the common ones | vivid dreams, “vibration”, a burning sensation in the skin | unknown |
Counterfeits of the original
In February 2026 the UK regulator found counterfeit Mounjaro pens at an online pharmacy.[11] The name on the packaging does not by itself prove authenticity.
Contraindications / who should be especially cautious
Contraindications in the FDA prescribing information and EMA product information
- personal or family history of medullary thyroid cancer, MEN 2 syndrome;
- allergy to tirzepatide or any component of the product.
Special caution
- pregnancy, planning a pregnancy, breastfeeding — there are no safety data;
- past pancreatitis, severe gastrointestinal disease, diabetic retinopathy;
- use of insulin or sulfonylureas, surgery under anaesthesia;
- children under 10 — not studied;
- eating disorders and older people with low muscle mass — expert opinion, not an item in the prescribing information;
- people without a medical indication — they did not take part in the trials.
Individual clinical cases
A young woman with type 2 diabetes and very high blood lipid levels had four attacks of acute pancreatitis over two years. After tirzepatide was prescribed, her metabolic markers improved, and there were no attacks over 12 months. The authors stress that this is a single-case observation, not proof.[23]
A 64-year-old woman with no history of pancreatitis was admitted a few days after a routine injection of tirzepatide, started for weight loss, with acute pancreatitis that progressed to a severe necrotising form and ended in death. This is the first fatal case of tirzepatide-associated pancreatitis described in the literature.[24][36]
Both cases involve the pancreas — but from opposite sides. That is why no general conclusions can be drawn from individual cases.
ZPHC products: what we could verify
Using the unique code on the packaging, you can confirm on the ZPHC website that the vial was made by ZPHC and is not a counterfeit of the brand. This protects against fakes but does not replace testing of the contents.
Third-party shops advertise the product for weight loss and bodybuilding — these are the sellers’ words, not the manufacturer’s.