MRK Pharmaceuticals · Large cap · Oncology · Vaccines · Thesis updated June 11, 2026

Merck is racing its patent cliffs

KEYTRUDA is still the center of Merck, with Q1 2026 sales of $7.9 billion plus $128 million from Keytruda Qlex.
WINREVAIR is the new proof point, reaching $525 million in Q1 2026 sales as uptake continued in the U.S., Japan, and Europe.
GARDASIL remains the biggest near-term problem, with sales down 19% in Q1 2026 and China revenue expected to be immaterial this year.
JANUVIA, JANUMET, and BRIDION lose U.S. exclusivity in mid-2026, so generic competition should hit late-2026 results.
Merck is cutting costs to reinvest in launches and pipeline work, but the stock does not look like a clear bargain.

01 Running thesis

A portfolio in transition

Merck is strong, but it is not a simple growth story. KEYTRUDA is still a huge cancer drug, and WINREVAIR is turning into a real new growth driver. In Q1 2026, WINREVAIR reached $525 million in sales, which gives investors something concrete to measure.

The problem is timing. JANUVIA and JANUMET lose U.S. market exclusivity in May 2026, Janumet XR follows in July 2026, and BRIDION also loses U.S. exclusivity in July 2026. Loss of exclusivity means cheaper generic drugs can enter, often causing sales to fall fast.

The bull case is that WINREVAIR, KEYTRUDA, WELIREG, Animal Health, and new pipeline drugs can more than offset those drops. The bear case is that the old products fall faster than the new ones rise, creating a revenue and earnings gap in late 2026 and 2027.

The hardest question is not whether Merck has good science. It does. The question is whether enough of that science turns into large products before the next major KEYTRUDA cliff gets closer.

May 2026→Q1 2026 confirmed both sides of the transition. WINREVAIR reached $525 million in sales, while Merck said GARDASIL revenue from China in 2026 should be immaterial and repeated the mid-2026 exclusivity losses for JANUVIA, JANUMET, and BRIDION.

Apr 2026▲The earnings call made the launch story more believable. WINREVAIR posted $525 million in global sales, and WELIREG rose to $199 million, partly offsetting the weak GARDASIL update.

Feb 2026▼The 2025 10-K made the GARDASIL problem worse, with full-year sales down 39% and China shipments still paused. It also gave clear 2026 timing for JANUVIA and BRIDION exclusivity losses.

Feb 2026→Management pointed to KEYTRUDA peak sales of about $35 billion by 2028, which helped the bull case. That was balanced by a 35% Q4 drop in GARDASIL sales and 2026 EPS guidance affected by a large Cidara acquisition charge.

Nov 2025▲The FDA approval of Keytruda Qlex helped Merck defend its core KEYTRUDA franchise. The same filing kept pressure on the thesis by confirming no further GARDASIL shipments to China for 2025 and a July 2026 BRIDION exclusivity loss.

Oct 2025▲WINREVAIR kept strong momentum at $360 million in quarterly sales, and Merck added ENFLONSIA and OHTUVAYRE to the commercial story. GARDASIL expectations became more cautious, with only modest near-term growth expected.

Aug 2025→The Q2 2025 filing confirmed strong WINREVAIR demand and ongoing GARDASIL weakness in China. Merck also announced a 2025 Restructuring Program aimed at about $3.0 billion in annual savings by 2027.

Jul 2025▲Merck said it would not resume GARDASIL shipments to China through at least year-end 2025, removing one near-term unknown. WINREVAIR reached $336 million in quarterly sales, and positive enlicitide Phase III data strengthened the pipeline story.

02 Business model

Science, sales, and reinvestment

Merck discovers, develops, makes, and sells medicines and vaccines. Most sales come from human health products sold to drug wholesalers, retailers, hospitals, governments, and health plans. A smaller but growing Animal Health business sells medicines, vaccines, and monitoring tools for livestock and pets.

The model works best when Merck owns protected drugs with strong demand. Patents and regulatory exclusivity help protect pricing and market share for a time. When that protection ends, generic or competing products can take a large share quickly.

Merck is trying to prepare for that cycle. Its 2025 Restructuring Program is meant to generate about $3.0 billion in annual savings by the end of 2027, with those savings reinvested into growth areas, late-stage pipeline work, and new launches.

That plan adds discipline, but it also shows the pressure. Merck must keep funding expensive research while replacing revenue from older products and handling pricing pressure from U.S. government programs.

03 Product portfolio

The drugs that matter most

Cash cow

KEYTRUDA

KEYTRUDA is Merck's lead cancer drug and the main profit engine. Q1 2026 sales were $7.9 billion, and management has framed the drug as central to growth through its peak years.

Option

Keytruda Qlex

Keytruda Qlex is the subcutaneous version of KEYTRUDA, meaning it is given by injection under the skin. It is a life-cycle move that may help Merck defend the franchise for longer.

Growth engine

WINREVAIR

WINREVAIR treats pulmonary arterial hypertension, a serious lung blood-pressure disease. Sales reached $525 million in Q1 2026, making it the clearest new launch success so far.

Cash cow

GARDASIL and GARDASIL 9

GARDASIL is Merck's HPV vaccine franchise, used to help prevent certain cancers and diseases. It is under pressure after a sharp China demand drop, with Q1 2026 sales down 19%.

Growth engine

WELIREG

WELIREG is part of the broader oncology portfolio. Q1 2026 sales rose 45% to $199 million, helped by continued launch uptake.

Cash cow

JANUVIA and JANUMET

JANUVIA and JANUMET are diabetes products now in decline. Merck expects to lose nearly all U.S. sales of Januvia and Janumet after loss of exclusivity.

Cash cow

BRIDION

BRIDION is used to reverse certain anesthesia effects after surgery. It loses U.S. market exclusivity in July 2026, and Merck expects U.S. sales to decline after that.

Steady

Animal Health

Animal Health sells veterinary medicines, vaccines, and health management tools. Q1 2026 sales grew, helped by both livestock and companion animal products.

04 Business segments

Mostly human health

Pharmaceutical89%modest

Animal Health11%growing fast

Mix is based on Q1 2026 reportable segment sales from Merck's Form 10-Q. It excludes $146 million of other corporate revenue, so the mix focuses on the two operating segments investors can track.

05 Risk factors

What could break the story

GARDASIL China does not recover

High impact · High odds

GARDASIL sales fell 19% in Q1 2026, mainly from lower demand in China and Japan. Merck paused China shipments in 2025 and now says any 2026 revenue from China tied to the revised supply deal will be immaterial. If demand outside China also weakens, the vaccine franchise could stay a drag for longer.

We watchQuarterly GARDASIL sales, especially ex-China growth and any change in China shipment commentary.

Mid-2026 generic shock

High impact · High odds

JANUVIA and JANUMET lose U.S. exclusivity in May 2026, Janumet XR in July 2026, and BRIDION in July 2026. Merck has said it expects to lose nearly all U.S. sales of Januvia and Janumet after loss of exclusivity. The first full quarter after generic entry will show how steep the hit is.

We watchQ3 2026 sales for JANUVIA, JANUMET, Janumet XR, and BRIDION.

WINREVAIR growth slows too soon

High impact · Medium odds

WINREVAIR is the strongest new launch proof point, but investors still do not know its steady run rate. If the drug plateaus near current levels, it may not offset the losses from older franchises. The bull case needs continued sequential growth.

We watchQuarterly WINREVAIR sales and international launch uptake.

Pricing pressure expands

Medium impact · High odds

The Inflation Reduction Act has already selected Januvia, Janumet, Janumet XR, and LENVIMA for government price setting. Merck also expects KEYTRUDA to be selected in 2027, with pricing changes becoming effective later. Lower prices can reduce sales and margins even when prescription demand stays healthy.

We watchCMS drug price setting lists, final negotiated prices, and Merck commentary on U.S. net pricing.

Pipeline spending fails to pay off

High impact · Medium odds

Merck is spending heavily to buy and build future products, including Cidara and the planned Terns deal noted in Q1 2026 filings. These deals can create large research and development charges before any sales appear. If late-stage data disappoints, the company may spend a lot without filling the revenue gap.

We watchPhase III readouts, regulatory decisions, and updates on acquired assets such as MK-1406 and TERN-701.

06 Quick answers

In one breath

What does Merck make?

Merck makes prescription medicines, vaccines, and animal health products. Its most important product is KEYTRUDA, a cancer drug, but it also sells vaccines like GARDASIL and newer medicines like WINREVAIR.

Why is Merck worried about patents?

When a drug loses exclusivity, generic versions can enter and take share. Merck faces this in mid-2026 for JANUVIA, JANUMET, Janumet XR, and BRIDION, which could pressure sales.

Why does WINREVAIR matter so much?

WINREVAIR is one of Merck's clearest new growth drivers. Its $525 million in Q1 2026 sales shows strong launch demand, but investors need to see whether that pace can keep rising.

What is the main debate on Merck stock?

The debate is whether Merck can replace older product sales fast enough. Bulls point to KEYTRUDA, WINREVAIR, oncology growth, and the pipeline. Bears point to GARDASIL weakness, mid-2026 generic losses, and the future KEYTRUDA cliff.