Reader’s guide · First edition · September 2026 · Revised October 1, 2026
Compounded Tirzepatide
A guide to the dual GIP / GLP-1 receptor agonist
Tirzepatide is the first medicine to activate two gut-hormone receptors at once: GLP-1 and GIP. Since 2022 it has produced the largest weight and blood-sugar reductions of any approved injectable. This guide explains how it works, what the trials showed, and what changes when the drug comes from a compounding pharmacy rather than a manufacturer's pen.
Who this is for
Written for adults who have been prescribed, or are considering, compounded tirzepatide from a licensed pharmacy. It is an educational summary of the published record, not medical advice, and it does not cover unregulated vials sold online without a prescription.
Tirzepatide is a 39-amino-acid synthetic peptide built on the backbone of GIP, a hormone released by the gut after a meal. It has been engineered to bind the receptors for both GIP and GLP-1, and a fatty-acid side chain lets it ride on albumin in the blood, which stretches its half-life to about five days. That is why it is injected once a week.
- Class
- Dual GIP and GLP-1 receptor agonist
- Route
- Subcutaneous injection, once weekly
- Half-life
- About 5 days
- Approved products
- Mounjaro (type 2 diabetes, 2022) · Zepbound (chronic weight management, 2023; obstructive sleep apnea with obesity, 2024)
- Maker
- Eli Lilly and Company
Compounded is not generic
There is no generic tirzepatide. A compounded preparation is made to order by a pharmacy from bulk active ingredient. It is not reviewed by the FDA for safety, effectiveness, or quality before it is sold. Section 05 explains what that means in practice.
GLP-1 and GIP are incretins: hormones the intestine releases when food arrives, telling the pancreas to prepare insulin. Each also has effects beyond the pancreas, and tirzepatide draws on both.
| GLP-1 receptor | GIP receptor | |
|---|---|---|
| Pancreas | Raises insulin and lowers glucagon, but only when blood sugar is high | Raises insulin after meals; supports glucagon when sugar is low |
| Stomach | Slows emptying, so meals feel larger and last longer | Little direct effect |
| Brain | Reduces appetite and food reward through the hypothalamus and brainstem | Acts on separate appetite circuits; in animals, dampens GLP-1 nausea |
| Fat tissue | Indirect, through weight loss | Improves how fat cells store and release lipids; improves insulin sensitivity |
Mechanistic summary drawn from the prescribing information and the pharmacology literature. The relative contribution of GIP in humans is still being worked out.
The practical result of hitting both receptors is that people eat less, feel full sooner, and handle glucose better, with weight loss that exceeds what GLP-1 agonists alone have achieved in head-to-head trials.
These numbers describe the branded product
Every trial below used Lilly's manufactured tirzepatide at a known dose and purity. No compounded tirzepatide preparation has been tested in a clinical trial. Treat these results as the ceiling of what the molecule can do, not a promise about any particular vial.
Mean body weight at 72 weeks, 15 mg, adults with obesity (SURMOUNT-1); placebo −3.1%
HbA1c at 40 weeks, 15 mg, type 2 diabetes (SURPASS-2); semaglutide 1 mg −1.9
Weight at 72 weeks, tirzepatide vs semaglutide 2.4 mg, head-to-head (SURMOUNT-5)
Reduction in apnea-hypopnea events at 52 weeks, obesity with sleep apnea (SURMOUNT-OSA)
Weight loss builds steadily over the first year and levels off between months 12 and 18. In SURMOUNT-1, roughly nine in ten participants on the top two doses lost at least 5% of their body weight, and about a third lost 25% or more. Blood pressure, triglycerides, and fasting insulin improved alongside weight.
The labeled schedule starts low to let the gut adapt, then climbs in fixed steps. Prescribers using compounded product generally follow the same ladder.
- Vial
- 30 mg lyophilized tirzepatide, pharmacy-dispensed
- Water added
- 1.5 mL bacteriostatic water
- Concentration
- 20 mg/mL. Use the same concentration for the whole course; a change between refills is the classic overdose path.
- Syringe
- 0.3 mL insulin syringe with half-unit marks for draws under 30 units; 1 mL syringe above that
| Weeks | Weekly dose | Draw | Units | Used per 4 weeks |
|---|---|---|---|---|
| 1–4 | 2.5 mg | 0.125 mL | 12.5 | 10 mg (1 vial; the rest is discarded at the beyond-use date) |
| 5–8 | 5 mg | 0.25 mL | 25 | 20 mg (1 vial) |
| 9–12 | 7.5 mg | 0.375 mL | 37.5 | 30 mg (1 vial exactly) |
| 13–16 | 10 mg | 0.5 mL | 50 | 40 mg (2 vials) |
| 17–20 | 12.5 mg | 0.625 mL | 62.5 | 50 mg (2 vials) |
| 21+ | 15 mg | 0.75 mL | 75 | 60 mg (2 vials) |
Half-unit draws are readable on a 0.3 mL syringe up to 30 units; above that, round to the nearest unit (a half unit is 0.1 mg, under 2% of the dose). Maximum labeled dose is 15 mg once weekly; many people stop at 5, 10, or 15 mg, and the right maintenance dose is the lowest one that works. A mixed vial is used within the pharmacy's beyond-use date, usually 28 days, so the 2.5 mg month wastes two-thirds of a vial; do not stretch it.
What each draw looks like · 1 mL (100-unit) U-100 insulin syringe
The plunger tip sits on the line for the dose. Units are marks on a U-100 syringe: 100 units is 1 mL. The picture assumes the concentration in the table above; a different amount of water changes every line.
- Inject under the skin of the abdomen, thigh, or back of the upper arm. Rotate sites each week.
- Same day each week, any time of day, with or without food. The day can be changed as long as at least 3 days separate two doses.
- Missed dose: take it within 4 days (96 hours). Past that, skip it and resume on the usual day. Never take two doses within 3 days.
- Oral contraceptives absorb less reliably for 4 weeks after starting and 4 weeks after each dose increase. Use a barrier or non-oral method during those windows.
- Expect the first noticeable appetite change within days and measurable weight change by week 4 to 8. Do not judge the drug on the 2.5 mg month.
Compounding is the pharmacy practice of preparing a drug for an individual patient. Federal law allows it, but compounding a copy of an FDA-approved drug is only permitted while that drug is in shortage or when a prescriber documents a patient-specific reason the approved product will not work.
| Date | Event |
|---|---|
| Dec 2022 | FDA lists tirzepatide in shortage; compounded copies become permissible |
| Dec 19, 2024 | FDA declares the shortage resolved |
| Feb 18, 2025 | Deadline for state-licensed (503A) pharmacies to stop compounding copies |
| Mar 19, 2025 | Deadline for outsourcing facilities (503B) to stop compounding copies |
| 2025 onward | Compounding continues only for documented, patient-specific need (for example, a dose or formulation the approved product does not offer, or an allergy to an excipient) |
The dosing-error problem
Approved tirzepatide comes in a pen that delivers one fixed dose. Compounded tirzepatide usually comes in a multi-dose vial drawn up with an insulin syringe marked in units. The FDA has received reports of patients taking 5 to 20 times the intended dose after confusing milligrams, milliliters, and units, or after a pharmacy changed concentration between refills. This is the single most important difference to understand.
- Concentration varies by pharmacy and can change between refills. Read the label every time.
- Insulin syringes are marked in units, where 100 units = 1 mL. Your dose in units depends entirely on the vial's concentration.
- Multi-dose vials carry a beyond-use date once punctured, set by the pharmacy under USP <797>. Refrigerate between 36 °F and 46 °F and discard on the date printed.
- Some compounders add vitamin B12, glycine, niacinamide, or other ingredients. The FDA has noted there is no safety or effectiveness data for these combinations. Ask why an additive is there.
- Only tirzepatide in the same chemical form used by the approved product is an eligible compounding ingredient. Ask the pharmacy to confirm the form and to provide a certificate of analysis for the batch.
- "Research use only" vials sold without a prescription are not compounded medicines. They are made without any pharmacy oversight and are outside the law and outside this guide.
Reading a vial: the dose arithmetic9
One formula covers every concentration. Volume in mL is the dose in mg divided by the concentration in mg/mL; units on an insulin syringe are that volume times 100.
units = (dose mg ÷ concentration mg/mL) × 100
At the 20 mg/mL standard in section 04, a 5 mg dose is 0.25 mL, which is 25 units on a U-100 syringe. Example at a different concentration: a 5 mg dose from a 10 mg/mL vial is 0.5 mL, which is 50 units.
| Weekly dose | 10 mg/mL (30 mg + 3 mL) | 20 mg/mL (30 mg + 1.5 mL) |
|---|---|---|
| 2.5 mg | 25 units (0.25 mL) | 12.5 units (0.125 mL) |
| 5 mg | 50 units (0.5 mL) | 25 units (0.25 mL) |
| 7.5 mg | 75 units (0.75 mL) | 37.5 units (0.375 mL) |
| 10 mg | 100 units (1 mL) | 50 units (0.5 mL) |
| 12.5 mg | two draws: 100 + 25 units | 62.5 units (0.625 mL) |
| 15 mg | two draws: 100 + 50 units | 75 units (0.75 mL) |
The 10 mg/mL option gives whole-unit draws through 10 mg but needs two injections at the top doses. Whichever concentration is dispensed, keep it for the whole course.
The common side effects are digestive, worst in the first weeks and after each dose increase, and usually fade. The serious ones are rare but need to be recognized early.
| Reaction | Tirzepatide | Placebo |
|---|---|---|
| Nausea | 25–29% | 9% |
| Diarrhea | 19–23% | 8% |
| Constipation | 11–17% | 6% |
| Vomiting | 8–13% | 2% |
| Abdominal pain | 9–10% | 5% |
| Injection-site reactions | 8% | 2% |
Managing them: smaller meals, stop eating when full, limit fat and alcohol early on, stay hydrated, and do not escalate the dose until the current one is comfortable.
Boxed warning: thyroid C-cell tumors
Tirzepatide caused thyroid C-cell tumors in rats. Whether it does so in humans is unknown. Do not use it with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. Report a neck lump, hoarseness, or trouble swallowing.
- Pancreatitis: severe, persistent abdominal pain, sometimes radiating to the back, with or without vomiting. Stop and seek care.
- Gallbladder disease: right-upper-abdominal pain, fever, or yellowing of the skin or eyes.
- Hypoglycemia when combined with insulin or a sulfonylurea; those doses usually need lowering.
- Dehydration and acute kidney injury after prolonged vomiting or diarrhea. Keep fluids up and seek care if unable to keep them down.
- Severe allergic reactions, including anaphylaxis and angioedema, have been reported.
- Diabetic retinopathy can worsen temporarily with rapid glucose improvement; people with existing retinopathy should be monitored.
- Slowed stomach emptying raises the risk of aspiration under general anesthesia or deep sedation. Tell every surgeon and anesthesiologist you take it.
- Mood: the Zepbound label advises monitoring for depression or suicidal thoughts, and stopping if they emerge.
- Pregnancy and breastfeeding: not for use. Discuss timing with a prescriber before trying to conceive.
A legitimate compounded prescription has a prescriber, a pharmacy, and a paper trail. These questions separate the pharmacies that take that seriously from the ones that do not.
- Who is the prescriber, and did they document why the approved product is not appropriate for me?
- Is the pharmacy licensed in my state? (Look it up on the state board of pharmacy website.) Is it a 503A pharmacy or a 503B outsourcing facility?
- What is the concentration in mg/mL, and will it be the same on every refill?
- What is my dose in mg, in mL, and in units, written on the label?
- What is the beyond-use date once the vial is opened, and how should it be stored?
- Can I see a certificate of analysis showing potency and sterility testing for this batch?
- Is the active ingredient the same form of tirzepatide used in Mounjaro and Zepbound?
- Are there any additives? If so, why?
- Who do I call with a question about drawing up a dose, and are they a pharmacist?
- Have I told my prescriber about insulin, sulfonylureas, oral contraceptives, thyroid history, pancreatitis, and any planned surgery?
Latest
Developments since this edition, newest first. Items here are dated and sourced; they update the guide without re-editing it.
FDA tells Empower Pharmacy its tirzepatide-niacinamide blend is a copy of an approved drug
FDA's warning letter says adding niacinamide to compounded tirzepatide (and B12 to semaglutide) does not make it meaningfully different from Mounjaro or Zepbound. FDA called the claimed differences 'pretextual', faulted templated 'significant difference' notes on prescriptions, and cited sterile-manufacturing failures.
FDA approves Mounjaro to reduce cardiovascular risk in type 2 diabetes
The approval rests on SURPASS-CVOT, a 13,299-person trial across 30 countries and the first head-to-head outcomes trial between incretin drugs: tirzepatide beat dulaglutide on major cardiovascular events with a hazard ratio of 0.92.
Mounjaro and Zepbound sales keep climbing as net prices fall
Second-quarter revenue was $9.9 billion for Mounjaro and $4.9 billion for Zepbound, up 91 and 46 percent on the year despite lower net prices; Lilly raised 2026 guidance to $85 to $87 billion.
Medicare Part D patients can now get Zepbound through the GLP-1 Bridge
A federal bridge program that took effect July 1 lets eligible Part D beneficiaries obtain Zepbound or the Foundayo pill for weight management, a use Medicare had not covered.
FDA sends 25 more warning letters over compounded tirzepatide and semaglutide claims
Telehealth firms were cited for advertising compounded GLP-1 drugs as equivalent to approved products or clinically proven. Separately, FDA's April proposal to permanently bar bulk compounding of tirzepatide closed for comment on July 30 with no final decision yet.
References
- 1.Zepbound (tirzepatide) injection. Prescribing information. Eli Lilly and Company. Current revision. https://pi.lilly.com/us/zepbound-uspi.pdf
- 2.Mounjaro (tirzepatide) injection. Prescribing information. Eli Lilly and Company. Current revision. https://pi.lilly.com/us/mounjaro-uspi.pdf
- 3.Coskun T, et al. LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: from discovery to clinical proof of concept. Mol Metab. 2018;18:3-14.
- 4.Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216.
- 5.Frías JP, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes (SURPASS-2). N Engl J Med. 2021;385(6):503-515.
- 6.Aronne LJ, et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). N Engl J Med. 2025.
- 7.Malhotra A, et al. Tirzepatide for the treatment of obstructive sleep apnea and obesity (SURMOUNT-OSA). N Engl J Med. 2024;391(13):1193-1205.
- 8.U.S. Food and Drug Administration. FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize. December 19, 2024. https://www.fda.gov/drugs/drug-safety-and-availability/fda-clarifies-policies-compounders-national-glp-1-supply-begins-stabilize
- 9.U.S. Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. Updated 2025. https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
- 10.U.S. Food and Drug Administration. Human drug compounding: sections 503A and 503B of the Federal Food, Drug, and Cosmetic Act. https://www.fda.gov/drugs/guidance-compliance-regulatory-information/human-drug-compounding
- 11.United States Pharmacopeia. General Chapter <797> Pharmaceutical Compounding — Sterile Preparations. 2023 revision.