How FDA Decisions Move Pharma and Biotech Stocks

FDA decisions move drug stocks because an approval or rejection changes, in one day, the expected revenue of a product that may be most of a company's value. The size of the move depends on that concentration: Replimune (REPL), with no approved product, fell 71% over two trading days after its second FDA rejection on April 10, 2026, while Ultragenyx (RARE) rose 12.6% on September 17, 2026, the day its gene therapy was approved ^{[1][2][11][14]}. For a large drugmaker such as Merck (MRK), whose top medicine alone brought in 47.6% of its second-quarter 2026 revenue, a single new approval is usually a small part of the whole ^[3].

What is a PDUFA date?

A PDUFA date is the target date by which the Food and Drug Administration aims to act on a drug application. The name comes from the Prescription Drug User Fee Act, under which drugmakers pay fees and the FDA commits to review deadlines. Under the current agreement, covering fiscal years 2023 through 2027, the FDA aims to act on 90% of new molecular entity drug applications and original biologics applications within 10 months of the 60-day filing date for a standard review, and within 6 months for a priority review ^[5]. In practice, that is about 12 months and 8 months after the application is submitted.

Companies usually disclose the date when the FDA accepts an application. Ultragenyx, for example, announced on April 2, 2026, that the FDA had accepted its resubmitted application for the gene therapy UX111 and set a PDUFA action date of September 19, 2026 ^[13]. The FDA can act before the date, as it did here two days early, or miss it, and the date is a goal rather than a legal deadline ^[5][14].

Approval versus complete response letter

At the end of a review, the FDA either approves the application or sends a complete response letter (CRL), a letter saying it cannot approve the application in its current form and listing the deficiencies. The FDA says CRLs are issued for various reasons, mostly safety and efficacy concerns, manufacturing deficiencies and bioequivalence issues ^[9]. A CRL is not always final: the company can fix the problems, run more studies and resubmit; the FDA aims to act on a resubmission within 2 months or 6 months, depending on its class ^[5].

For investors, what the CRL says matters as much as the fact of it. A manufacturing deficiency at a third-party plant can be fixed in months; a request for a new clinical trial can mean years and more money. Until 2025, the market mostly had to rely on the company's own summary. On July 10, 2025, the FDA published more than 200 CRLs issued for applications submitted between 2020 and 2024, and noted that a 2015 analysis by FDA researchers found sponsors' announcements left out 85% of the FDA's safety and efficacy concerns ^[9].

Advisory committees

Before some decisions, the FDA convenes an advisory committee of outside experts, which discusses the data in public and often votes. A vote can move a stock sharply, but the FDA says the committees' recommendations are advice and do not bind the agency; the final decision rests with the FDA ^[10].

How much do biotech stocks move on FDA news?

The move depends on how much of the company's value rides on the decision and how surprised the market is. Three 2026 cases show the range:

Source: company filings and news reports ^{[11][12][14][15]}; prices from DataPorium daily closes ^[1][2][4].

Replimune: when one drug is the company

Replimune received a second CRL for its melanoma immunotherapy RP1 (vusolimogene oderparepvec), used with nivolumab, on April 10, 2026; its first had come in July 2025 ^[11][12]. The company's chief executive said that without timely accelerated approval, development of RP1 would not be viable, and the company announced job cuts and a large reduction in its US manufacturing operations ^[12]. The shares closed at $5.91 on April 9, $4.76 on April 10 and $1.70 on April 13, the next trading day: a 71.2% decline in two sessions ^[1]. They had already fallen from $7.80 on April 7 to $5.89 on April 8 ^[1].

Ultragenyx: an approval that beat the request

Ultragenyx had asked for accelerated approval of UX111; on September 17, 2026, the FDA instead granted standard full approval of the therapy, now named Fayuvi, as the first approved treatment for Sanfilippo syndrome type A, a fatal neurodegenerative disease in children. The company also received a priority review voucher with the approval ^[13][14]. The stock rose from $12.88 to $14.50 that day, a gain of 12.6% ^[2].

Why do small biotechs move more than big pharma?

The main reason is concentration. A company with no product on the market is valued almost entirely on the expected profits of its pipeline, so a decision on its lead drug can remove or confirm most of that value at once. A large drugmaker sells dozens of products, and a newly approved drug starts with little or no revenue.

Merck shows the scale. In the second quarter of 2026, Merck reported revenue of $16.61 billion. Its cancer drug Keytruda brought in $7.90 billion, or 47.6% of the total, and the next largest product, the Gardasil vaccines, $1.17 billion, or 7.0% ^[3]. Newer medicines were a few percent each: Winrevair $588 million (3.5%) and Ohtuvayre $204 million (1.2%) ^[3]. When the FDA approved Merck's Lipfendra on July 16, 2026, the first oral PCSK9 inhibitor for lowering LDL cholesterol, Merck's shares closed up 3.3% that day and were little changed the next ^[4][15].

Other factors add to the swing at small companies:

• Cash: a company without product revenue may need to raise money after a rejection, often at a lower share price, diluting existing shareholders.
• Expectations: a stock that already reflects a likely approval may barely move on the news, or fall, while a surprise moves it most.
• Odds: most drug programs never reach approval, so the market discounts unapproved drugs heavily until the decision.

How often does the FDA approve new drugs?

The FDA's drug center approved 50 novel drugs in 2024 and 46 in 2025 ^[7][8]. In 2026, it had approved 46 by October 9, against 33 by the same date in 2025 and 34 in 2024 ^[6][7][8]. These counts cover new drugs reviewed by the Center for Drug Evaluation and Research; many vaccines and gene therapies, such as Fayuvi, are reviewed by a separate center for biologics and are not included.

Source: FDA, Novel Drug Approvals for 2024, 2025 and 2026, as of October 9, 2026 ^[6][7][8].

Approval at the FDA is the last step of a long funnel. In a study of 406,038 clinical trial records covering more than 21,000 compounds from 2000 to 2015, Wong, Siah and Lo found that 13.8% of drug development programs eventually led to approval, and 3.4% in oncology ^[16]. That is why an unapproved drug is valued as a probability, and why the decision day carries so much weight.

The fewer products a drugmaker sells, the more of its value rides on each FDA decision, and the larger the move on approval or rejection.

How to follow FDA decisions

1. Find the date: companies disclose PDUFA dates in press releases and 8-K filings, as Ultragenyx did on April 2, 2026 ^[13].
2. Check the concentration: compare the drug's potential with the company's current revenue by product, as in Merck's breakdown on DataPorium ^[3].
3. Read the letter, not only the headline: the FDA now publishes CRLs, so the deficiencies can be compared with the company's summary ^[9].
4. Watch for an advisory committee: its vote is non-binding but public ^[10].

Company prices, filings and revenue by product are on DataPorium's stock pages, and drug market data on the healthcare drugs page.

Key takeaways

• The FDA aims to act on 90% of new drug applications within 10 months of the 60-day filing date for standard reviews and 6 months for priority reviews ^[5].
• Replimune, with no approved product, fell 71.2% in two trading days after its second CRL on April 10, 2026 ^[1][11].
• Ultragenyx rose 12.6% on September 17, 2026, when Fayuvi won full approval two days before its PDUFA date ^[2][14].
• At Merck, Keytruda alone was 47.6% of second-quarter 2026 revenue, while newer drugs were 1% to 4% each ^[3].
• The FDA's drug center approved 46 novel drugs by October 9, 2026, after 46 in all of 2025 and 50 in 2024 ^[6][7][8].

Frequently asked questions

What happens on a PDUFA date?

It is the FDA's goal date to approve the application or issue a complete response letter. The FDA can act earlier, as with Ultragenyx's Fayuvi, approved on September 17, 2026, two days before its September 19 date ^[13][14].

What is a complete response letter from the FDA?

It is the FDA's letter saying an application cannot be approved in its current form, listing the deficiencies to fix. Since July 2025, the FDA has published CRLs, starting with more than 200 letters from 2020 to 2024 applications ^[9].

Are FDA advisory committee votes binding?

No. The FDA says committee recommendations are advice that does not bind the agency, and the final decision rests with the FDA ^[10].

What percentage of drugs get FDA approval?

A study of clinical trials from 2000 to 2015 found that 13.8% of drug development programs that entered testing in people eventually won approval, and 3.4% in oncology ^[16].

Sources & References

1. [1] DataPorium Replimune (REPL) stock page (daily prices)
2. [2] DataPorium Ultragenyx (RARE) stock page (daily prices)
3. [3] DataPorium Merck (MRK) revenue by product (second quarter 2026)
4. [4] DataPorium Merck (MRK) stock page (daily prices)
5. [5] U.S. Food and Drug Administration, PDUFA Reauthorization Performance Goals and Procedures, Fiscal Years 2023 Through 2027 (accessed October 13, 2026)
6. [6] U.S. Food and Drug Administration, Novel Drug Approvals for 2026 (content current as of October 9, 2026)
7. [7] U.S. Food and Drug Administration, Novel Drug Approvals for 2025 (accessed October 13, 2026)
8. [8] U.S. Food and Drug Administration, Novel Drug Approvals for 2024 (accessed October 13, 2026)
9. [9] U.S. Food and Drug Administration, FDA Embraces Radical Transparency by Publishing Complete Response Letters (July 10, 2025)
10. [10] U.S. Food and Drug Administration, Advisory Committees: Critical to the FDA's Product Review Process (accessed October 13, 2026)
11. [11] Replimune Group, Form 8-K (April 10, 2026)
12. [12] Pharmacy Times, Replimune Receives Second CRL for RP1 With Nivolumab for Treatment of Advanced Melanoma (April 13, 2026)
13. [13] Ultragenyx Pharmaceutical, Form 8-K (April 2, 2026)
14. [14] Ultragenyx Pharmaceutical, Form 8-K (September 17, 2026)
15. [15] TCTMD, FDA Approves Enlicitide, an Oral PCSK9 Inhibitor, for LDL-Lowering (July 16, 2026)
16. [16] Wong, Siah and Lo, Estimation of Clinical Trial Success Rates and Related Parameters, Biostatistics 20(2), 2019