Tirzepatide (Zepbound, Mounjaro)

Summary

Tirzepatide is an FDA approved once weekly injectable that activates the receptors for two gut hormones, GIP and GLP-1, which boost insulin and curb appetite. It is one molecule sold under two brand names: Mounjaro for type 2 diabetes (2022) and, since August 2026, lowering cardiovascular risk (heart attack, stroke, or cardiovascular death) in adults with type 2 diabetes at high cardiovascular risk, and Zepbound for chronic weight management (2023) and obstructive sleep apnea (breathing that repeatedly stops during sleep) in obesity (2024). In the 72 week SURMOUNT-1 trial, adults with obesity lost a mean 20.9% of body weight on 15 mg versus 3.1% on placebo, and in the head to head SURMOUNT-5 trial it beat semaglutide, 20.2% versus 13.7%.

What is Tirzepatide?

Tirzepatide is a dual GIP and GLP-1 receptor agonist (39 amino acid peptide, acylated for once weekly dosing). It is also known as Mounjaro, Zepbound, LY3298176, compounded tirzepatide, Zepbound KwikPen, Mounjaro KwikPen.

How does it work?

Tirzepatide is a single peptide that activates the GIP receptor and the GLP-1 receptor. GLP-1 receptor activation increases glucose dependent insulin release, suppresses glucagon, slows gastric emptying, and reduces appetite. GIP receptor activation appears to add further appetite and insulin effects and may improve tolerability. The C20 fatty diacid moiety binds albumin for a half life of about 5 days.

What does the evidence say about Tirzepatide?

Large randomized controlled trials in both obesity and type 2 diabetes. SURMOUNT-1 (n = 2,539) showed 15.0%, 19.5%, and 20.9% mean weight loss at 5, 10, and 15 mg over 72 weeks versus 3.1% with placebo. SURPASS-2 (n = 1,879) showed superior HbA1c and weight reduction versus semaglutide 1 mg. A dedicated cardiovascular outcomes trial (SURPASS-CVOT) reported non-inferiority to dulaglutide in 2025. FDA added a cardiovascular risk reduction indication to Mounjaro in August 2026 on the basis of this trial (hazard ratio 0.92 versus dulaglutide, non-inferior but not superior).

Human evidence

SURMOUNT-1: 2,539 adults with obesity or overweight without diabetes, 72 weeks; mean weight change minus 15.0% (5 mg), minus 19.5% (10 mg), minus 20.9% (15 mg) versus minus 3.1% (placebo); 91% of the 15 mg group lost at least 5%. SURPASS-2: 1,879 adults with type 2 diabetes; HbA1c reductions of 2.01 to 2.30 percentage points versus 1.86 with semaglutide 1 mg, and weight change of minus 7.6 to minus 11.2 kg versus minus 5.7 kg. Additional SURMOUNT and SURPASS trials cover diabetes with obesity, obstructive sleep apnea, and maintenance after weight loss.

Animal evidence

Preclinical rodent studies established the dual agonist pharmacology and appetite effects. Rodent studies also showed thyroid C cell tumors, the basis for the boxed warning shared with other GLP-1 agonists; this has not been reproduced in humans.

Key studies

Conditions studied

Is Tirzepatide legal in the United States?

FDA and compounding status

FDA approved products (Mounjaro May 2022, Zepbound November 2023). FDA declared the tirzepatide shortage resolved on December 19, 2024; compounding by 503A pharmacies had to stop by February 18, 2025 and by 503B outsourcing facilities by March 19, 2025, except for a documented patient specific clinical need. FDA has warned about unapproved compounded and counterfeit tirzepatide products. On April 30, 2026 FDA proposed not to include tirzepatide on the 503B bulks list; that proposal was not final as of September 2026. Adding a vitamin such as B12 or niacinamide does not by itself make a compounded GLP-1 different from the approved drug. Under FDA's April 1, 2026 policy update, such a combination may be treated as essentially a copy when the strengths are within 10% of approved products and the route is the same, unless a prescriber documents a real difference for the individual patient. A September 2026 FDA warning letter applied this to semaglutide and tirzepatide vitamin combinations, said high production volume suggested the claimed differences were a pretext, and questioned significant-difference statements picked from preset menus on prescribing platforms.

WADA status

Not WADA prohibited. Not named on the current prohibited list. Athletes should still confirm against the list in force for their season.

Regulatory timeline

1. Sep 18, 2026FDA

   FDA warning letter treats GLP-1 plus vitamin combinations as essentially copies

   In a warning letter dated September 18, 2026 and posted September 22, FDA said compounded tirzepatide with niacinamide and semaglutide with cyanocobalamin (vitamin B12) appeared to be essentially copies of approved drugs, that the volume produced suggested the claimed differences were a pretext, and that significant-difference statements were repeated verbatim across many records or chosen from preset menus on prescribing platforms. The letter's findings are specific to one pharmacy, but they apply FDA's April 1, 2026 policy that a combination within 10% of approved strengths by the same route may be treated as essentially a copy without a documented prescriber determination.

   Source: FDA warning letter to a compounding pharmacy on semaglutide and tirzepatide vitamin combinations (September 18, 2026)
2. Aug 28, 2026FDA

   FDA approves Mounjaro to reduce cardiovascular risk in adults with type 2 diabetes

   FDA added an indication for Mounjaro to lower the risk of major adverse cardiovascular events (cardiovascular death, non-fatal heart attack, or non-fatal stroke) in adults with type 2 diabetes who are at high risk for these events. The approval rests on SURPASS-CVOT, in which tirzepatide was non-inferior to dulaglutide (hazard ratio 0.92, 95.3% CI 0.83 to 1.01) but did not show superiority.

   Regulatory: FDA approvedSource: Manufacturer press release: FDA approves Mounjaro (tirzepatide) to reduce cardiovascular risk in adults with type 2 diabetes (August 28, 2026)
3. Apr 30, 2026FDA

   FDA proposes to keep semaglutide, tirzepatide and liraglutide off the 503B bulks list

   FDA proposed not to include semaglutide, tirzepatide or liraglutide on the 503B bulks list, after tentatively finding no clinical need for outsourcing facilities to compound them from bulk. The notice was published May 1, 2026, and the comment period was extended to July 30, 2026. The proposal was not final as of September 2026. It does not change the 503A rules for patient specific compounding.

   Source: Federal Register 2026-08552: List of Bulk Drug Substances for Which There Is a Clinical Need Under Section 503B
4. Mar 19, 2025FDA

   503B grace period for compounded tirzepatide ends

   FDA's enforcement discretion for 503B outsourcing facilities compounding tirzepatide ended, closing the shortage-based pathway for compounded tirzepatide.

   Source: FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize (Wayback Machine capture of the FDA page, March 13, 2026)
5. Feb 18, 2025FDA

   503A grace period for compounded tirzepatide ends

   FDA's enforcement discretion for 503A pharmacies compounding tirzepatide ended. After this date 503A pharmacies may not compound copies of Mounjaro or Zepbound on shortage grounds.

   Source: FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize (Wayback Machine capture of the FDA page, March 13, 2026)
6. Dec 20, 2024FDA

   FDA approves Zepbound for obstructive sleep apnea in adults with obesity

   FDA approved Zepbound (tirzepatide) for moderate to severe obstructive sleep apnea in adults with obesity, the first drug approved for that indication.

   Regulatory: FDA approvedSource: FDA approves first medication for obstructive sleep apnea
7. Dec 19, 2024FDA

   FDA reaffirms the tirzepatide shortage is resolved and sets grace periods

   After reconsideration, FDA confirmed the tirzepatide shortage was resolved and announced enforcement discretion periods: 503A pharmacies until February 18, 2025 and 503B outsourcing facilities until March 19, 2025.

   Source: FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize (Wayback Machine capture of the FDA page, March 13, 2026)
8. Oct 11, 2024Other

   FDA agrees to reconsider the tirzepatide shortage decision after compounder lawsuit

   After the Outsourcing Facilities Association sued over the October 2 resolution decision, FDA told the court it would reconsider the tirzepatide shortage determination and would not take enforcement action against compounders in the interim.

   Source: FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize (Wayback Machine capture of the FDA page, March 13, 2026)
9. Oct 2, 2024FDA

   FDA declares the tirzepatide shortage resolved

   FDA announced that the shortage of tirzepatide injection (Mounjaro and Zepbound) was resolved, meaning compounders could no longer rely on the shortage to prepare copies of the approved products.

   Source: FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize (Wayback Machine capture of the FDA page, March 13, 2026)
10. Nov 8, 2023FDA

    FDA approves Zepbound (tirzepatide) for chronic weight management

    FDA approved tirzepatide injection (Zepbound) for chronic weight management in adults with obesity or overweight with at least one weight-related condition.

    Regulatory: FDA approvedSource: FDA approves new medication for chronic weight management
11. Dec 2022FDA

    FDA lists tirzepatide injection on the drug shortage list

    In December 2022 FDA added tirzepatide injection (Mounjaro) to its drug shortage list, opening the door to compounded tirzepatide under FDA's shortage compounding policies.

    Source: FDA drug shortages database
12. May 13, 2022FDA

    FDA approves Mounjaro (tirzepatide) for type 2 diabetes

    FDA approved tirzepatide injection (Mounjaro), the first dual GIP and GLP-1 receptor agonist, to improve glycemic control in adults with type 2 diabetes.

    Regulatory: FDA approvedSource: Drugs@FDA: Mounjaro (tirzepatide) NDA 215866

Full tracker for Tirzepatide or the category-wide tracker.

Tirzepatide dose schedule on the FDA label

Doses below are quoted from the FDA label for its approved uses, plus the doses used in the pivotal trials where noted. The prescriber sets the dose; PeptideAgent does not recommend doses or protocols.

SURMOUNT-1 and the FDA labels (Zepbound and Mounjaro): start 2.5 mg subcutaneously once weekly for 4 weeks, then increase in 2.5 mg steps every 4 weeks as tolerated to a maintenance dose of 5, 10, or 15 mg weekly. The 2.5 mg dose is for initiation only and is not a maintenance dose. Each step comes after at least 4 weeks on the current dose. Zepbound maintenance for obstructive sleep apnea is 10 or 15 mg weekly. The maximum is 15 mg weekly in adults and 10 mg weekly in children 10 and older on Mounjaro. Both brands come as 2.5, 5, 7.5, 10, 12.5, and 15 mg single-dose pens or vials, plus 4 dose KwikPens and multi-dose vials.

Routes reported

Zepbound and Mounjaro side effects in trials

Side effects

Interactions

Contraindications

How do people access Tirzepatide legally?

Typical cost: Manufacturer list price is up to 1,086.37 USD per fill for Zepbound and 1,112.16 USD for Mounjaro (checked 2026-09-22). Manufacturer self-pay Zepbound vials and KwikPen cost 299 USD per month at 2.5 mg, 399 at 5 mg, 499 at 7.5 mg, and 699 at 10 mg and above, with a 449 USD on-time refill offer for the 7.5 mg and higher KwikPen through 2026. With commercial insurance a savings card can bring a covered prescription to 25 USD, and eligible Medicare Part D enrollees pay 50 USD per month for the Zepbound KwikPen under the Medicare GLP-1 Bridge (July 2026 to December 2027). A study published in 2025 found compounded tirzepatide advertised at a median 330 USD for the first month during the shortage; compounding is now limited to patient specific needs.

• Tirzepatide cost by channel
• Rules by state
• Verified provider directory

Compare Tirzepatide

• Zepbound vs Mounjaro
• Semaglutide vs tirzepatide
• Tirzepatide vs cagrilintide
• Tirzepatide vs dulaglutide
• Tirzepatide vs liraglutide
• Tirzepatide vs mazdutide
• Tirzepatide vs retatrutide
• Tirzepatide vs survodutide

Frequently asked questions

Decisions about starting, stopping, or combining any treatment belong with a licensed clinician who knows your history.

From the blog

• Compounded tirzepatide in 2026: legality, cost, and safety

  The tirzepatide shortage ended in December 2024 and routine compounded copies ended in 2025. What is still lawful, what it cost, FDA safety warnings, and how to check a pharmacy.

• Microdosing GLP-1s and tirzepatide: what the evidence says

  No trial has tested microdosing semaglutide or tirzepatide. What the labels say about dose steps and why they exist, FDA's dosing-error warnings, and what to ask a prescriber.

• What is peptide therapy? What clinics sell, what is legal, and what works

  Peptide therapy means three different things: FDA-approved drugs, compounded prescriptions, and research-only products. Here is how to tell them apart, what the evidence shows, and what it costs.

• SURMOUNT-5 explained: tirzepatide vs semaglutide head to head

  The first head-to-head obesity trial of tirzepatide and semaglutide found a 20.2% vs 13.7% weight loss gap at 72 weeks. What it tested, what it did not, and what it means for access.

• Are peptide injections safe? What is known and unknown

  FDA-approved peptide injections have documented side effects on their labels. Compounded and research-only peptides add unknowns: sterility, identity, dose accuracy, and contamination.

• Do GLP-1 patches work? What they contain and what the evidence says

  No FDA-approved GLP-1 patch exists. Here is why GLP-1 drugs cannot pass through skin from a sticker, what patch ingredients have been tested by mouth, and how to read patch reviews.

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Sources

Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.