How Zepbound Overtook Wegovy

Wegovy had a two-year head start, a household-name sibling in Ozempic, a jingle people could hum and the entire cultural conversation about weight-loss drugs pointed at it. Zepbound launched in November 2023 and was ahead of it in new US prescriptions by March 2024.

This is how that happened, with the dates and the numbers attached.

When exactly did Zepbound pass Wegovy?

Twice, on two different measures, about a year apart.

New prescriptions: In the week ending March 8, 2024, Zepbound recorded 77,590 new US prescriptions, ahead of Wegovy for the first time, according to IQVIA data published by JPMorgan and reported by Reuters [1]. New prescriptions measure who is starting, which is the leading indicator. That same week Wegovy still led on total weekly prescriptions, by 25,307 - which is exactly why the two measures get confused.

Total prescriptions: Total scripts include everyone refilling, so the incumbent holds that line longer. By the week ending April 18, 2025, trade coverage of IQVIA data put Zepbound near 339,000 total weekly prescriptions, clearly in the lead [2].

By the end of 2025, Lilly was willing to put its name on the bigger claim. Its February 23, 2026 press release called Zepbound “the most prescribed weight management medication in 2025,” citing IQVIA’s National Prescription Audit as of December 2025 [3]. That is a manufacturer’s claim built on a third-party dataset, which is worth saying out loud, but the underlying dataset is the same one everyone in the industry uses.

The market-share version of the story is blunter still: Lilly’s share of the US incretin market reached about 60.1% by March 2026, up from roughly 45% a year earlier [4].

Why did Zepbound win? Was it the trial results?

Partly, and this is the reason Lilly leads with in every ad.

SURMOUNT-5 was an open-label head-to-head study of tirzepatide against semaglutide. Participants on tirzepatide lost about 50 pounds, or 20.2% of body weight, against about 33 pounds, or 13.7% on semaglutide [3].

That is an unusual thing to have in this market. Most drug comparisons are indirect, assembled from separate trials with different populations. A direct head-to-head gives a marketing department a number it can put on television, and Lilly did, repeatedly - including in the Zepbound spot that ran around Super Bowl LX in February 2026 [5].

It also gave Novo Nordisk something to sue about, which we will get to.

Did Zepbound win because it was advertised more?

No, and this is the most counterintuitive part of the story.

Reuters reported in January 2026 that Novo Nordisk spent close to $500 million on US advertising for Wegovy and Ozempic in the first nine months of 2025 [6]. Brand-level detail from the same data: Wegovy $316 million, Ozempic $169 million, Zepbound $131 million, Mounjaro $83 million [7]. Lilly’s combined spend of roughly $214 million was less than half of Novo’s.

Over that same period, Lilly’s market share went up and Novo’s went down.

That is not an argument that advertising does not work. Lilly’s advertising is effective, and measurably so. The analytics firm EDO found pharma ads during 2025-26 NFL regular season games were about 104% more effective than average pharma spots in prime-time broadcast and cable, and within that, Zepbound was the single most effective pharma brand of the season, at 519% above the average pharma advertiser [18]. It is an argument that in a market where the products are genuinely different, the product data moved more volume than the media budget.

What did prescribers have to do with it?

A lot, and this is the least-discussed factor.

IQVIA’s analysis of the launch found that at 12 months post-launch, Mounjaro and Zepbound had reached about four times as many unique prescribers as Ozempic and Wegovy had at the same point in their launches [8]. Tirzepatide did not spread through specialist obesity clinics. It spread through ordinary primary care.

IQVIA’s broader numbers give the scale: US GLP-1 prescriptions went from about 2.5 million a month before October 2022 to more than 9 million a month by the end of 2024, and about 11 million unique US GLP-1 patients were counted in the second quarter of 2025 [8].

How did price change the race?

By turning a prescription drug into something with a posted retail price.

Lilly launched Zepbound single-dose vials in August 2024 with a $399 starting-dose cash price, against a list price above $1,000. Senator Bernie Sanders called that a “modest step forward” and pointed out that Mounjaro still cost $1,069 a month in the US against $485 in the United Kingdom and $94 in Japan [9].

Then the cash channel kept getting cheaper and easier:

• June 2025: every approved vial dose available through LillyDirect self-pay.
• October 29, 2025: those vials became available for in-store pickup at about 4,600 Walmart pharmacies.
• November 6, 2025: Lilly’s agreement with the Trump administration put Zepbound on the TrumpRx site and promised eligible Medicare beneficiaries a $50 monthly copay.
• December 1, 2025: cash prices cut again, to $299 for the lowest dose and up to $449 for higher doses [10].
• February 2026: multi-dose KwikPens added to the self-pay menu.

Lilly said more than 1 million patients accessed its treatments through LillyDirect in 2025, and that one in three new patients starting a branded weight management medicine that year was prescribed Zepbound self-pay vials [3].

That is how a company wins customers who never get past a prior authorization form.

Political pressure on the price did not stop with Sanders’s 2024 statement, though it moved from tirzepatide specifically to the class. A Senate HELP Committee minority staff report in April 2026 returned to GLP-1 pricing, citing Foundayo’s fast approval and the gap between US and overseas prices as evidence that announced federal deals had not yet lowered what Americans pay [20].

What happened when CVS Caremark dropped Zepbound?

This is the one moment where the trend reversed, and it is the best natural experiment anyone has run on this market.

On May 1, 2025, the pharmacy benefit manager CVS Caremark announced that Zepbound would come off its standard preferred formularies effective July 1, 2025, making Wegovy the preferred obesity drug for an estimated 25 million to 30 million covered lives [11].

One detail gets lost in most retellings: the decision applied only to the obesity indication. Tirzepatide remained available on the same formularies as Mounjaro for people with type 2 diabetes. What changed was which brand of the same molecule an insurer would pay for, and for which condition.

The effect showed up immediately. Truveta analyzed electronic health records covering 1,647,238 patients and more than 6 million GLP-1 prescriptions and found that between June and July 2025:

• Tirzepatide’s monthly share growth slowed by about half, from roughly +0.06 percentage points a month to +0.03.
• Semaglutide’s monthly share growth accelerated about fivefold, from roughly +0.02 points a month to +0.1.
• First-time tirzepatide prescriptions fell month over month for the first time in nearly a year, while first-time semaglutide prescriptions rose 4.9%, the strongest monthly increase in more than a year [11].

Switching moved even more sharply than prescribing. In July 2025, 9.6% of patients on anti-obesity tirzepatide switched to a different drug, more than a 16-fold increase over the earlier 2025 average, and more than eight in ten of those who switched moved to semaglutide [11].

Truveta labeled the findings preliminary and not peer reviewed, and noted that prescribing is not the same as dispensing. A follow-up analysis presented at the AMCP annual meeting in April 2026 found the spike was short-lived: switching stayed elevated at roughly 1.6% through September 2025 and returned to baseline in October.

The human version of that data filled r/Zepbound for a year: people who had lost 60 or 70 pounds being moved to a different medicine, then stalling, then posting about it.

In September 2025, patients filed a proposed class action against CVS Caremark over the decision [12]. And on May 28, 2026, Caremark reversed course: Zepbound returns as an additional preferred option alongside Wegovy effective October 1, 2026, with eligible commercially insured patients able to pay as little as $25 a month [13]. In the same announcement Caremark lifted its new-to-market block on Lilly’s oral Foundayo, effective earlier - June 1, 2026 - for plans that had approved coverage of it.

One caution that matters more than any of this: being on a formulary is not the same as being covered. Employers make the final decision about what their plan pays for.

Is this fight over?

No. Three things are still moving.

The lawsuit. On July 21, 2026, Novo Nordisk sued Eli Lilly in the US District Court for the District of New Jersey under the Lanham Act and state false-advertising law, alleging that Lilly’s national Zepbound and Mounjaro advertising misleads patients by comparing Lilly’s highest doses (10 mg and 15 mg tirzepatide) against the 1.7 mg and 2.4 mg Wegovy doses used in SURMOUNT-5, while never mentioning the 7.2 mg Wegovy dose the FDA approved in March 2026 [14]. Lilly responded that Novo’s newer high-dose product has no head-to-head trial supporting it and that Lilly has not made those claims in paid advertising. Novo’s chief executive Mike Doustdar defended the suit in August 2026: “Competition has to be fierce, but I also think competition has to be fair” [15]. These are allegations, not findings.

Pills. Lilly’s injectable lead does not extend to oral medicines. Novo’s Wegovy pill launched in January 2026 and drew 3,071 US prescriptions in its first week, then 18,410 in its second. Lilly’s Foundayo, approved April 1, 2026 and shipping from April 6, drew 1,390 in its launch week and 3,707 in its second - roughly a fifth of Novo’s pace at the same stage [19]. Trade coverage in August 2026 described Foundayo’s second quarter as disappointing even as injectable tirzepatide kept growing [16]. Doustdar said in August 2026 that the Wegovy pill had passed 5 million US prescriptions [15].

The next molecule. Lilly is pushing toward retatrutide, a next-generation obesity medicine, and has told investors that is where its growth goes after tirzepatide.

What is the plain-English summary?

Zepbound overtook Wegovy because it had better head-to-head trial results, reached far more prescribers at launch, priced aggressively for people paying cash, and kept supply flowing. One insurer’s formulary decision briefly reversed the trend and then got reversed itself. Advertising money went the other way and did not change the outcome.

And the scale of what tirzepatide became is easy to lose in the brand fight: in the first quarter of 2026, Mounjaro alone passed Keytruda to become the best-selling drug in the world [17].

Sources

1. Reuters, “Lilly weight-loss drug Zepbound new US prescriptions surpass Wegovy for first time,” March 15, 2024. https://www.reuters.com/business/healthcare-pharmaceuticals/lilly-weight-loss-drug-zepbound-new-us-prescriptions-surpass-wegovy-first-time-2024-03-15/
2. pharmaphorum, “Lilly hit as PBM drops Zepbound, but retains Wegovy,” May 2, 2025. https://pharmaphorum.com/news/lilly-hit-pbm-drops-zepbound-retains-wegovy
3. Eli Lilly, “Zepbound, the most prescribed weight management medication in 2025, now available in multi-dose KwikPen,” February 23, 2026. https://investor.lilly.com/news-releases/news-release-details/zepbound-tirzepatide-most-prescribed-weight-management
4. Investing.com, “Eli Lilly Q1 2026 slides: incretin dominance drives 56% revenue surge,” April 30, 2026. https://www.investing.com/news/company-news/eli-lilly-q1-2026-slides-incretin-dominance-drives-56-revenue-surge-93CH-4650699
5. Xtalks, “New Zepbound commercial ‘Watch This’ highlights long-term impact,” February 2026. https://xtalks.com/new-zepbound-commercial-watch-this-highlights-long-term-impact-4708/
6. Reuters, “Novo’s Wegovy and Ozempic US advertising spend doubles rival Eli Lilly, data shows,” January 28, 2026. https://www.reuters.com/business/media-telecom/novos-wegovy-ozempic-us-advertising-spend-doubles-rival-eli-lilly-data-shows-2026-01-28/
7. GuruFocus, “Novo Nordisk doubles US ad spend on Wegovy, Ozempic,” January 29, 2026. https://www.gurufocus.com/news/8559264/novo-nordisk-doubles-us-ad-spend-on-wegovy-ozempic
8. IQVIA, “Obesity deep dive: the unparalleled launch success of Mounjaro and Zepbound,” September 23, 2025. https://www.iqvia.com/locations/united-states/blogs/2025/09/obesity-deep-dive-the-unparalleled-launch-success-of-mounjaro-and-zepbound
9. Office of Senator Bernie Sanders, statement on Eli Lilly’s decision to lower the starter price of Zepbound, August 27, 2024. https://www.sanders.senate.gov/press-releases/news-sanders-statement-on-eli-lillys-decision-to-lower-the-starter-price-of-blockbuster-weight-loss-drug-zepbound/
10. Eli Lilly, “Lilly lowers the price of Zepbound single-dose vials,” December 1, 2025. https://investor.lilly.com/news-releases/news-release-details/lilly-lowers-price-zepboundr-tirzepatide-single-dose-vials
11. Truveta, “Impact of the CVS GLP-1 formulary change: trends in prescribing,” September 5, 2025. https://www.truveta.com/blog/research/research-insights/impact-of-the-cvs-glp-1-formulary-change-trends-in-prescribing/
12. CNN, “A pharmacy benefit manager stopped covering a GLP-1 for obesity. Now there’s a lawsuit,” September 5, 2025. https://www.cnn.com/2025/09/05/health/cvs-caremark-glp-1-lawsuit
13. NBC DFW / Associated Press, “CVS Caremark will cover Lilly’s weight loss drug Zepbound again after patient backlash,” May 28, 2026. https://www.nbcdfw.com/news/national-international/cvs-caremark-will-cover-lillys-weight-loss-drug-zepbound/4029504/
14. The Hill, “Novo Nordisk sues rival Eli Lilly over weight loss drug advertising,” July 21, 2026. https://thehill.com/policy/healthcare/5981384-novo-nordisk-sues-eli-lilly-advertising/
15. CNBC, “Novo Nordisk CEO defends lawsuit against Eli Lilly: ‘Competition has to be fair,’” August 12, 2026. https://www.cnbc.com/2026/08/12/novo-nordisk-ceo-defends-lawsuit-against-eli-lilly.html
16. Fierce Pharma, “Lilly’s obesity pill Foundayo ‘disappointed’ in Q2, as injectables continue to boom,” August 5, 2026. https://www.fiercepharma.com/pharma/lillys-obesity-pill-foundayo-disappointed-q2-injectables-continue-boom
17. The Boston Globe, “Lilly’s Mounjaro overtakes Keytruda as world’s top-selling drug,” May 6, 2026. https://www.bostonglobe.com/2026/05/06/business/lillys-mounjaro-overtakes-keytruda-worlds-top-selling-drug/
18. MediaPost, “Report: Lilly and Zepbound led pharma ad effectiveness during NFL season,” February 4, 2026 (EDO data). https://www.mediapost.com/publications/article/412518/report-lilly-zepbound-led-pharma-ad-effectivene.html
19. Fierce Pharma, “The oral GLP-1 tracker: launch trajectories for Lilly’s Foundayo and Novo’s Wegovy pill” (IQVIA data via Jefferies), updated 2026. https://www.fiercepharma.com/pharma/oral-glp-1-tracker-launch-trajectories-lilly-foundayo-novo-wegovy-pill
20. US Senate HELP Committee, minority staff report, “Promises made, promises broken: prescription drug prices continue to skyrocket,” April 16, 2026. https://www.help.senate.gov/imo/media/doc/help_minority_drug_pricing_report.pdf

This page describes a market, not a treatment plan. Trial results described here are what studies reported in their populations; they are not a prediction about any individual. Talk to a healthcare provider about whether any of these medicines is right for you.