Tirzepatide: A Year-by-Year History of Mounjaro and Zepbound

If you have tried to follow the news about tirzepatide, you have probably run into the same confusion everyone else does. It has two American brand names. It has four approved uses. It spent two years in shortage and then became the best-selling medicine in the world. British newspapers call the weight-loss version by the name Americans use for the diabetes version.

This article lays the whole thing out in order, one year at a time, with a source for every date. It is a news history, not medical guidance. Nothing here tells you whether tirzepatide is right for you or what dose anyone should take. Those are conversations for a healthcare provider.

What is tirzepatide, in one paragraph?

Tirzepatide is a once-weekly injection made by Eli Lilly. It imitates two gut hormones at once, GIP and GLP-1, which is why it is described as a dual agonist. Semaglutide, the molecule in Ozempic and Wegovy, imitates only GLP-1. That second hormone is the main technical difference between the two drugs, and it is the usual explanation offered for why tirzepatide has produced more weight loss in trials.

Lilly sells the same molecule under two names in the United States. Mounjaro is the type 2 diabetes brand. Zepbound is the weight management and sleep apnea brand. Same drug, same strengths, different labels [1][2].

What happened in 2022, the year tirzepatide was approved?

The year began with tirzepatide as a diabetes drug that some analysts thought might also work for weight.

On April 28, 2022, Lilly released the first results from SURMOUNT-1, a trial of 2,539 adults with obesity or overweight who did not have diabetes. Average weight loss over 72 weeks ran from 16.0% at the lowest dose to 22.5% at the highest [3]. Nothing in the obesity drug field had come close to that outside of surgery, and the number reset what people expected a medicine could do.

Two weeks later, on May 13, 2022, the FDA approved Mounjaro for adults with type 2 diabetes under priority review [1]. The label the agency posted that day describes a starting dose of 2.5 mg once weekly stepping up over months to a maximum of 15 mg, and carries a boxed warning about thyroid C-cell tumors seen in rodents [2].

In October the FDA granted tirzepatide fast track designation for obesity, the procedural step that let Lilly file its weight-loss application in pieces [4].

Then came the problem that defined the next two years. On December 16, 2022, the FDA added Mounjaro to the national drug shortage list, roughly seven months after launch [5]. Under federal law, a shortage listing is what allows compounding pharmacies to make copies of an approved drug. That single line in a database created the compounded tirzepatide market.

What changed in 2023, when a second brand arrived?

Lilly spent 2023 filling in the evidence and building factories.

In April, SURMOUNT-2 showed average weight loss of up to 15.7% in people who had type 2 diabetes as well as obesity [6]. In June, phase 2 data landed for two pipeline drugs that would dominate later years: orforglipron, a daily pill, and retatrutide, a triple agonist that produced up to 24.2% weight loss in mid-stage testing [7]. In July, SURMOUNT-3 reported a total of 26.6% weight loss counting a 12-week lifestyle lead-in, and SURMOUNT-4 reported, less comfortably, rapid regain in people switched to placebo.

In August, the first “stomach paralysis” lawsuits named both Novo Nordisk and Eli Lilly. In September, Lilly began suing med spas, wellness clinics and compounding pharmacies over products sold as tirzepatide, opening an enforcement campaign that is still running.

The headline event came on November 8, 2023, when the FDA approved Zepbound for chronic weight management in adults with obesity, or adults with overweight plus at least one weight-related condition [8][9]. Lilly set the list price at $1,059.87 a month, below Wegovy’s list price at the time [10]. On the same day, British regulators extended the Mounjaro license to weight management, which is the origin of the transatlantic naming confusion [10].

Zepbound reached US pharmacies on December 5, 2023.

Why was 2024 the year of shortage, sleep apnea and the first price cut?

Supply was the story for the first half of the year. Most doses of both brands sat in “limited availability” through the spring, and the shortage listing kept the compounded market legal.

Two things broke the pattern.

First, on April 17, 2024, Lilly reported that tirzepatide reduced the severity of obstructive sleep apnea by up to nearly two thirds in two trials of adults with OSA and obesity [11]. Sleep apnea had no approved drug treatment at all.

Second, on August 27, 2024, Lilly began selling single-dose vials of the two lowest Zepbound doses directly to people paying cash, at $399 and $549 a month, roughly half the pen price [12]. That was aimed squarely at compounded tirzepatide, which had been selling for a few hundred dollars a month, and it started a price ladder that Lilly has walked down ever since.

In October the FDA declared the tirzepatide shortage resolved [13]. Compounders sued within days, the agency briefly agreed to reconsider, and then on December 19, 2024 it reaffirmed the decision and set wind-down deadlines [14].

The year closed with two more firsts. On December 4, Lilly reported the topline from SURMOUNT-5, the first randomized head-to-head trial against Wegovy: 20.2% average weight loss on tirzepatide against 13.7% on semaglutide [15]. On December 20, the FDA approved Zepbound for moderate to severe obstructive sleep apnea in adults with obesity, the first drug ever approved for the condition [16][17].

How did 2025 crack Medicare open and start a formulary fight?

January brought a quiet but important decision. Medicare is barred by statute from covering drugs used for weight loss, but CMS confirmed on January 8, 2025 that Part D plans could cover Zepbound when it is prescribed for obstructive sleep apnea, because that is a medically accepted indication rather than weight loss [18]. It was the first Medicare opening any obesity drug had found.

Three months later the administration declined to finalize a broader Biden-era proposal that would have let Medicare cover obesity drugs outright.

In May the full SURMOUNT-5 results published in the New England Journal of Medicine, confirming the head-to-head advantage [19]. The same month brought the sharpest commercial blow of the year: CVS Caremark named Wegovy its preferred obesity drug on its largest commercial template and excluded Zepbound, moving hundreds of thousands of patients from one drug to the other [20]. Lawsuits and open letters followed.

In July, the SURPASS-CVOT trial reported that tirzepatide was non-inferior to Trulicity on major adverse cardiovascular events in adults with type 2 diabetes, with lower all-cause death [21]. That result became the basis of an approval a year later.

By October, tirzepatide had passed Merck’s Keytruda to become the world’s best-selling medicine, at $10.1 billion for the third quarter against Keytruda’s $8.1 billion. That milestone belongs to the molecule across both brands together, not to Zepbound on its own [22]. In November, Lilly and Novo Nordisk struck most-favored-nation pricing deals with the White House that set Medicare pricing and opened coverage, and on November 21 Lilly became the first drugmaker valued at a trillion dollars.

December brought the first phase 3 result for retatrutide, TRIUMPH-4, showing weight loss of up to 28.7% (71.2 lbs) at 68 weeks along with relief from knee osteoarthritis pain, and a US pediatric approval extending Mounjaro to children aged 10 and older with type 2 diabetes.

What has 2026 brought so far?

February 23, 2026 was a good day for Lilly and a bad one for its rival. The FDA cleared the multi-dose Zepbound KwikPen, which packs a month of weekly doses into one device [23]. On the same day, Novo Nordisk’s next-generation CagriSema failed to beat Zepbound in a head-to-head obesity trial, and Novo’s shares fell sharply.

On April 1, 2026 the FDA approved Foundayo, the brand name for orforglipron, the first once-daily GLP-1 pill for weight loss that can be taken at any time of day without food or water restrictions. Two weeks after approving it, the agency asked Lilly for additional safety evaluation covering liver and cardiovascular signals, an unusual post-approval request.

In May, the SURMOUNT-MAINTAIN trial published in The Lancet, showing that people who had reached their weight on higher-dose tirzepatide largely held it on a lower maintenance dose [24]. The same month, CVS Caremark announced it would restore Zepbound to its formulary from October 1 and add Foundayo.

On August 27, 2026, the FDA approved Mounjaro to reduce the risk of major cardiovascular events in adults with type 2 diabetes [25][26]. That removed the last big clinical argument that only semaglutide had proven heart benefit, and it means tirzepatide now holds four US indications across its two brands.

What has stayed the same the whole time?

Three things, and they are worth holding onto when the headlines move fast.

The drug works while you take it. SURMOUNT-4 in 2023 and the maintenance trials in 2026 both point the same way: weight comes back after stopping, and the current evidence treats tirzepatide as an ongoing treatment rather than a course. What that means for any individual is a question for a healthcare provider.

Access, not efficacy, has been the binding constraint. Shortage in 2022 and 2023, compounding in 2024, formulary exclusion in 2025, Medicare rules throughout. Almost every major story in this history is about who can get the drug and at what price.

And the naming problem has never gone away. Mounjaro and Zepbound are the same medicine. If you are reading British or European coverage, “Mounjaro” there usually means what “Zepbound” means here [10].

Sources

1. FDA approves Lilly’s Mounjaro (tirzepatide) injection — PR Newswire / Eli Lilly, May 13, 2022
2. MOUNJARO (tirzepatide) injection — original FDA label — FDA, May 13, 2022
3. Lilly’s tirzepatide delivered up to 22.5% weight loss in SURMOUNT-1 — PR Newswire / Eli Lilly, April 28, 2022
4. Lilly receives FDA fast track designation for tirzepatide in obesity — PR Newswire / Eli Lilly, October 6, 2022
5. US FDA flags shortage of Eli Lilly’s new diabetes drug Mounjaro — Reuters, December 16, 2022
6. Lilly’s tirzepatide achieved up to 15.7% weight loss in SURMOUNT-2 — PR Newswire / Eli Lilly, April 27, 2023
7. Lilly’s phase 2 retatrutide results published in NEJM — PR Newswire / Eli Lilly, June 26, 2023
8. FDA approves Lilly’s Zepbound (tirzepatide) for chronic weight management — PR Newswire / Eli Lilly, November 8, 2023
9. ZEPBOUND (tirzepatide) injection — original FDA label — FDA, November 8, 2023
10. Eli Lilly gets FDA approval to sell Mounjaro as obesity drug called Zepbound — STAT, November 8, 2023
11. Tirzepatide reduced sleep apnea severity by up to nearly two-thirds — PR Newswire / Eli Lilly, April 17, 2024
12. Lilly releases Zepbound single-dose vials — PR Newswire / Eli Lilly, August 27, 2024
13. Lilly’s weight-loss drug removed from FDA’s shortage list — Reuters, October 2, 2024
14. FDA reaffirms decision to erase Eli Lilly’s tirzepatide from shortage list — Fierce Pharma, December 19, 2024
15. Lilly’s Zepbound superior to Wegovy in head-to-head trial — PR Newswire / Eli Lilly, December 4, 2024
16. FDA approves Zepbound as the first prescription medicine for moderate-to-severe obstructive sleep apnea — PR Newswire / Eli Lilly, December 20, 2024
17. Eli Lilly’s obesity drug Zepbound approved to treat sleep apnea — STAT, December 20, 2024
18. Medicare can now cover Eli Lilly’s Zepbound for sleep apnea — CNBC, January 8, 2025
19. Complete SURMOUNT-5 results published in the New England Journal of Medicine — PR Newswire / Eli Lilly, May 11, 2025
20. Novo strikes deal giving Wegovy preferred access on CVS Caremark formulary — Fierce Pharma, May 1, 2025
21. Lilly’s Mounjaro demonstrated cardiovascular protection in head-to-head trial — PR Newswire / Eli Lilly, July 31, 2025
22. Eli Lilly’s weight loss and diabetes drug tops Keytruda as world’s best-selling medicine — STAT, October 30, 2025
23. Zepbound now available in multi-dose KwikPen — PR Newswire / Eli Lilly, February 23, 2026
24. Tirzepatide for maintenance of bodyweight reduction (SURMOUNT-MAINTAIN) — The Lancet, May 12, 2026
25. FDA approves Lilly’s Mounjaro to reduce cardiovascular risk in adults with type 2 diabetes — Eli Lilly, August 28, 2026
26. FDA approval letter, Mounjaro supplements 44 and 45 — FDA, August 27, 2026
27. FDA set to review Sandoz’s generic GLP-1s — Reuters, June 29, 2026