Amarin shares fell 67% after a federal judge in Nevada invalidated the patents on Vascepa, a drug the FDA approved in 2012. [6][7] Biogen shares rose 58% at midday on June 7, 2021, the day the FDA approved Aduhelm. [8] Each move took one trading day. Neither move tells you what an approval or a patent ruling is worth over the life of a drug.
This article separates two questions that headlines blend together. The first question is how a stock reacts on the day of a regulatory or legal event. The second question is how value builds, or fails to build, across the years of market exclusivity. The published evidence we reviewed gives different answers to each question.
We cite every source by number. We label every calculated figure as analysis. We use the data fields that DrugPatentWatch tracks as a guide to the patent and exclusivity dates that matter. [17] We send readers to primary sources for the dates themselves.
The Short Answer: Do Drug Approvals and Patent Rulings Move Stocks?
Yes, but the size depends on the type of event and the type of company. Settlement news moved brand stock prices by about 3.5% to 6% on average in two event studies. [1][2] A single court ruling moved Amarin by 67%. [6] Trial-result news for seven large firms produced median moves of about 1% to 2%. [3]
What do studies show about stock reactions to FDA approval?
The effect is small and often priced in before the announcement. One thesis in the Texas Digital Library repository studied 400 approval events at 11 pharmaceutical companies over 23 years. It found positive and statistically significant abnormal returns on the next day. It found mostly insignificant cumulative abnormal returns in pooled regressions. It found no evidence of information leakage before the events. [19]
That repository page does not list an author or a year, and we could not confirm peer review. We give it less weight than the journal and working-paper sources below.
A second source points the same way. In a 2000 to 2009 sample of oncology drugs, stock prices before FDA decisions did not differ between companies that later received positive decisions and companies that received negative decisions. [4]
What do studies show about patent rulings and settlements?
The effect is larger. Panattoni built a dataset of all Paragraph IV decisions and estimated that these decisions have large value consequences for brand firms. [5] Drake and co-authors found that brand stock prices rose about 6% on average when a settlement included a reverse payment. [1] A later study found a 3.5% average rise for settlements it classed as potentially collusive. [2]
The Five Findings That Matter
Each finding below stands alone and carries its own source.
Across 68 brand-generic settlements since 1993, brand stock prices rose about 6% on average at announcement when the deal included a reverse payment. Settlements without one showed no significant effect. [1]
Across 64 settlements from 2014 to 2023, the 17 classed as potentially collusive raised brand stock prices by about 3.5% on average. The authors estimate $3.1 billion to $3.2 billion per year in added U.S. purchaser spending. [2]
Across 24 trial announcements at seven large firms, the median cumulative abnormal return on negative news was -2.0% over the window from two days before to the event day. The median on positive news was +0.8%. [3]
In an oncology sample, stocks of companies with positive phase III trials rose 13.7% on average in the 120 days before the announcement. Stocks of companies with negative trials fell 0.7%. [4]
The average market exclusivity period for drugs is about 12 to 14 years, as reported by Grabowski and co-authors and cited in a 2019 slide deck. [14]
Methodology: How We Built This Analysis
What data did we review?
We reviewed event-study papers, news coverage of two court rulings and one FDA approval, FDA guidance pages, the U.S. Code, one SEC filing and the DrugPatentWatch dashboard. The events span 1993 through 2025. [1][15]
How did we select and combine records?
We kept a source when it reported a measurable stock reaction, a statutory limit or a dated event. We dropped sources that gave opinion without data. The two Drake papers use settlement samples that may overlap, so we report them side by side and never add them together. [1][2]
How did we calculate derived figures?
Ratios, shares of counts and dollar scenarios are our own arithmetic on reported numbers. We round to one decimal place. Each derived figure carries the word “derived” or “analysis” in the text or table.
What are the limits?
We did not run our own event study and we did not pull price data. Event windows differ across studies. The Hwang sample has 24 events and covers large firms only. [3] Amarin and Biogen are selected cases, not a random sample. The Biogen figure is a midday move reported by a news outlet, not a verified closing return. [8]
Definitions: Event Study, Abnormal Return, Exclusivity and Paragraph IV
What is an event study?
An event study measures how a stock moves around a dated news item, compared with what the stock would have done without the news. The authors choose a window, such as two days before to two days after.
What is a cumulative abnormal return?
A cumulative abnormal return (CAR) is the sum of daily returns above or below the expected return across the event window. Hwang used a 300-trading-day estimation window to set the expected return. [3]
What is the difference between a patent and regulatory exclusivity?
A patent term is 20 years from the U.S. filing date. [10] Regulatory exclusivity is a separate FDA protection that starts at approval. The two run on different clocks, and a drug can have one, both or neither.
New chemical entity and clinical investigation exclusivity
FDA lists 5 years for new chemical entity exclusivity and 3 years for new clinical investigation exclusivity. [10]
Orphan and pediatric exclusivity
FDA lists 7 years for orphan drug exclusivity. Pediatric exclusivity adds 6 months to existing patents and exclusivities. [10]
Patent term extension
Under 35 U.S.C. 156, the extension based on the regulatory review period may not exceed five years. The total of the remaining term and the extension may not exceed fourteen years after approval. [11]
Reference table: exclusivity types and lengths
Protection
Length
Starts
Source
Patent term
20 years
U.S. filing date
[10]
Patent term extension
Up to 5 years, 14 years after approval in total
Applies to term remaining at approval
[11]
New chemical entity exclusivity
5 years
Approval
[10]
New clinical investigation exclusivity
3 years
Approval
[10]
Orphan drug exclusivity
7 years
Approval
[10]
Pediatric exclusivity
6 months added
Added to existing protections
[10]
Biologic reference product exclusivity
12 years (4 before a biosimilar application, 8 more before approval)
Approval
[14]
Why Does FDA Approval Move Large Drug Stocks So Little?
Because the market has usually priced in the outcome. By the time the FDA acts, trial data, advisory discussions and company disclosures are public. The approval removes one remaining doubt. It adds little new information.
What does the oncology sample show about run-ups?
Rothenstein and co-authors studied January 2000 to January 2009. Their sample had 23 positive and 36 negative phase III cancer-drug trials. It also had 41 positive and 9 negative FDA regulatory decisions. [4]
In the 120 days before trial announcements, positive-trial stocks rose 13.7% on average and negative-trial stocks fell 0.7%. [4] The gap is 14.4 percentage points (derived). Pre-decision prices before FDA actions did not separate the two groups. [4]
Is a pre-announcement run-up evidence of leakage?
Not by itself. Feuerstein and Ratain answered the study by noting that market capitalization 120 days before announcements was about 80 times greater for companies with positive trials. They argued that the market anticipates outcomes, so negative results may not have been a surprise. [4] The authors also list selection bias and a small number of companies as caveats. [4]
What do the sample shares imply about approval odds?
In the Rothenstein sample, 41 of 50 FDA decisions were positive. That is 82% (derived). Only 23 of 59 phase III readouts were positive. That is 39% (derived). Analysis: the sample suggests most uncertainty ends at the trial readout, not at the FDA decision. The sample is selected, so we do not extend this ratio to all drugs.
What does the approval thesis add?
It adds a second view. The thesis found a significant positive next-day return but mostly insignificant cumulative returns. [19] Novartis and Abbott showed significant positive abnormal and cumulative returns around the event day and the day after. [19] A firm-level result of this kind fits a simple reading: a drug matters more to a company when it is large relative to the company.
Clinical Trial News vs. Patent News: Which Moves Prices More?
Neither source set we reviewed compares the two on the same firms and dates. We can compare what each reports. Trial news at large firms moved prices by about 1% to 2% at the median. [3] Settlement news moved brand prices by 3.5% to 6% on average. [1][2]
What did Hwang find for trial results at large firms?
Hwang (2013) studied 24 announcements of phase 1 to 3 results at seven large U.S.-listed firms from January 2011 to May 2013. The sample had 16 positive and 8 negative events. It excluded compounds already approved by the FDA or EMA, so it is not an approval study. [3]
Window (trading days)
Positive events (n=16)
Negative events (n=8)
Size ratio, negative to positive (derived)
-2 to 0
+0.8% (P = 0.02)
-2.0% (P = 0.04)
2.5
-2 to +1
+0.4% (P = 0.33)
-1.7% (P = 0.03)
4.3
-2 to +2
+0.8% (no P reported)
-1.2% (P = 0.04)
1.5
-1 to 0
+0.9% (P = 0.02)
-0.7% (P = 0.01)
0.8
-1 to +1
+0.5% (P = 0.28)
-1.3% (P = 0.04)
2.6
Source: Hwang (2013) [3]. The ratio column is our arithmetic.
Why do negative results move prices more?
Hwang describes the reaction as asymmetric: negative results produced larger and more persistent declines. [3] In four of the five windows above, the negative median is larger in size than the positive median (derived). In the shortest window, it is not. With 8 negative events, we treat the ratio as a direction, not a precise number.
Does firm size change the answer?
Hwang warns that the results may not generalize to smaller biotech firms or non-U.S. companies. [3] The Amarin case below shows why that warning matters.
Amarin and Vascepa: A 67% Drop From One Patent Ruling
Vascepa (icosapent ethyl) is an Amarin drug that the FDA approved in 2012 for lowering high triglycerides. In December 2019, the FDA cleared it to reduce the risk of events such as heart attacks and strokes. [7]
What did the Nevada district court decide?
Judge Miranda Du of the U.S. District Court for the District of Nevada ruled for generic makers Dr. Reddy’s Laboratories and Hikma, who had filed abbreviated new drug applications for generic Vascepa. The court invalidated Amarin’s patent protection on the drug. [6] Amarin shares fell 67% on Nasdaq after the ruling. [6]
What did the Federal Circuit decide?
On September 3, 2020, the Federal Circuit upheld the district court. The ruling found six Vascepa patents invalid for obviousness. [7] Amarin shares fell by nearly a third after oral argument the day before, and fell further after the decision. [7]
What did the rulings mean for generic entry?
The rulings made it more likely that Hikma and Dr. Reddy’s could launch generic Vascepa. Hikma said it was working towards a launch, and the FDA had approved its generic in May. [7] Amarin said the generic makers might not be able to readily make large supplies. [7]
What did the stock lose in total?
BioPharma Dive reported that Amarin had lost about 80%, or roughly $7 billion, of its value since late 2019. [7] Analysis: $7 billion at 80% implies a starting value of about $8.75 billion (derived). The ruling came about eight years after approval (derived from [6] and [7]). The court decision arrived 5 months before the appeals decision (derived).
Aduhelm: A 58% Approval Pop That Did Not Last
What happened on approval day?
The FDA approved Biogen’s Aduhelm (aducanumab) on Monday, June 7, 2021, the first Alzheimer’s treatment approved in 18 years. Shares jumped 58% in midday trading after a halt for the news. [8] An outside FDA advisory panel had earlier said more data was needed, and some experts questioned the evidence of meaningful benefit. [8]
What happened afterward?
On January 31, 2024, Biogen announced it would stop developing and selling Aduhelm. Rights reverted to Neurimmune. Biogen said the decision was not related to safety or efficacy. It cited a strategic review that found no partners or external financing, and it chose to build around Leqembi with Eisai. [9] The article on the decision noted less than $6 million in sales after approval. [9]
What does the case teach?
Analysis: approval is one clock, and commercial uptake is another. An accelerated approval came with a required post-approval trial. [8] The one-day price move priced the approval. It could not price the sales that followed.
Case comparison table
Drug
Company
Event
Reported reaction
What followed
Source
Vascepa (icosapent ethyl)
Amarin
D. Nev. ruling for Dr. Reddy’s and Hikma, 2020
-67% after ruling
Federal Circuit affirmed on Sept. 3, 2020; six patents invalid as obvious
[6][7]
Aduhelm (aducanumab)
Biogen
FDA accelerated approval, June 7, 2021
+58% at midday
Discontinued Jan. 31, 2024
[8][9]
How Does Paragraph IV Litigation Work, and When Does It Hit the Stock?
A Paragraph IV filing is a generic applicant’s challenge to a listed brand patent. The legal steps run on fixed deadlines, so an analyst can build a calendar of likely news dates. [12]
What is the Paragraph IV timeline?
Step
Deadline or length
Source
Applicant sends notice letter
Within 20 days after FDA says the ANDA is ready for substantive review
[12]
Brand files suit to trigger the stay
Within 45 days of receiving the notice
[12]
Automatic stay of ANDA approval
30 months from receipt of the notice
[12]
First applicant’s marketing exclusivity
180 days
[12]
The 30-month stay equals 2.5 years (derived). The earliest ruling dates therefore sit inside a window an analyst can estimate from the notice date.
What is the 30-month stay?
If the brand sues within 45 days, it gets an automatic stay of ANDA approval that runs from the date the patent owner receives the notice. [12]
What is 180-day exclusivity?
The first ANDA applicant to challenge the brand patents gets 180 days of marketing exclusivity before other generics can enter. [12] FDA calls this the Patent Challenge type of 180-day exclusivity. [10]
What did Panattoni find about Paragraph IV decisions?
Panattoni built a dataset of all Paragraph IV decisions. The decisions skew toward the highest-revenue drugs and periods of significant patent protection. [5] The study estimates large value consequences for brand firms. [5] Analysis: the cases that reach decision are the ones where the money is, which is why a ruling can move a share price more than a settlement of a minor product.
Settlement Announcements: What Does Pay-for-Delay Do to a Stock Price?
What did the 2014 study find?
Drake, Starr and McGuire classified 68 brand-generic settlements from 1993 onward by whether the deal had an indicated reverse payment. Brand stock prices rose about 6% on average at announcement for deals with a reverse payment. Deals without one showed no significant effect. [1]
What did the 2024 study find?
Statistic: across 64 brand-generic settlements from 2014 to 2023, the 17 classed as potentially collusive raised brand stock prices by about 3.5% on average, and the authors estimate $3.1 billion to $3.2 billion per year in added U.S. purchaser spending, or about $12 billion per year across the industry. (Drake & McGuire, NBER Working Paper 33196; Journal of Health Economics, vol. 103, 2025) [2]
Settlements with no sign of collusion had no significant effect, which suggests the market had expected them. [2] The authors disclose funding from the Blue Cross Blue Shield Association. [2]
Analysis: 17 of 64 is 26.6% (derived). Over ten years, $3.1 billion to $3.2 billion per year is about $31 billion to $32 billion in total (derived, assuming a constant annual figure).
Scenario analysis: what do 3.5% and 6% mean in dollars?
The table applies the two reported averages to three assumed market capitalizations. The capitalizations are hypothetical. The table is not a forecast for any company.
Assumed market cap
At +3.5% [2]
At +6% [1]
$10 billion
$0.35 billion
$0.60 billion
$50 billion
$1.75 billion
$3.00 billion
$200 billion
$7.00 billion
$12.00 billion
Does a price rise prove the settlement is anticompetitive?
No. The authors read the rise as a market estimate of expected profit from delayed generic entry. [1][2] The classification of “potentially collusive” rests on announcement descriptions and later information. [2] Other readers may classify a deal differently.
The Decade-Long Marathon: How Long Does Exclusivity Really Last?
Why is effective patent life shorter than 20 years?
Clinical trials and regulatory review use up patent time before launch. Grabowski and Vernon describe the 1984 law that restores part of the lost time and also makes generic competition possible at patent expiry. [13]
How long is the average market exclusivity period?
Grabowski, Long, Mortimer and Boyo report market exclusivity periods that average about 12 to 14 years, as shown in a 2019 slide deck by Long. [14] The nominal 20-year patent term is 6 to 8 years longer than that average (derived). The two measures start at different dates, so we use the gap only as a rough guide.
Scenario analysis: how does patent term extension work in numbers?
The cap on extension is five years, and the post-approval total may not exceed fourteen years. [11] The table uses three hypothetical drugs. It assumes the full five-year extension is earned and applies to the same patent.
Hypothetical drug
Patent filed before approval
Term left at approval
Plus 5-year extension
After 14-year cap
A
8 years
12 years
17 years
14 years
B
10 years
10 years
15 years
14 years
C
14 years
6 years
11 years
11 years
Analysis: the extension helps most when a patent was filed late in development. Drugs with early patents hit the 14-year cap.
What happens when exclusivity ends? The Humira example
AbbVie’s FY2024 Form 10-K states that Humira has faced competition from biosimilar products in the United States following the loss of exclusivity in 2023. [18] The filing ties the competitive change to a dated exclusivity event. An analyst who tracks that date years ahead can model the exposure before it appears in results.
How many drugs get approved each year?
CDER approved 46 novel drugs in 2025. [15] Analysis: on about 250 trading days, that is roughly one novel approval every 5.4 trading days (derived, assuming 250 days). A small annual count limits the number of clean events any one study can use.
Humira After Exclusivity: What a Dated Revenue Cliff Looks Like
Humira net revenues were $8.993 billion worldwide in 2024. That is a 37.6% drop on a reported basis. [20] U.S. revenues were $7.142 billion, down 41.3%. International revenues were $1.851 billion, down 17.5%. [20]
What was Humira revenue before the decline?
The AbbVie release does not state 2023 revenue. Analysis: backing out the 37.6% decline gives about $14.4 billion for 2023 (derived: 8.993 divided by 0.624). We treat that as an estimate, not a reported figure. A reader who needs the exact number should take it from AbbVie’s FY2023 Form 10-K.
Why did the U.S. fall faster than international sales?
The 10-K states that U.S. biosimilar competition began after the loss of exclusivity in 2023. [18] The U.S. decline of 41.3% is larger than the international decline of 17.5%. [20] Analysis: the gap fits the dated U.S. event. The data do not prove the cause, because pricing and coverage changes also affect these lines.
How large is the U.S. share of the 2024 total?
U.S. revenue was 79.4% of the 2024 total (derived: 7.142 divided by 8.993). A drug with a high U.S. share is more exposed to a U.S. loss-of-exclusivity date.
What does a revenue cliff do to the “overnight” idea?
It shows the opposite time scale. The Amarin drop took one day. [6] The Humira decline appears in annual results, one reporting period at a time. [20] Analysis: litigation news compresses value change into hours, while loss of exclusivity spreads it across years.
Why Do “Overnight Millionaire” Stories Mislead?
They show the day of the move and hide the ten years around it. The evidence we reviewed supports four corrections.
Correction one: the move may have started before the news
In the oncology sample, positive-trial stocks gained 13.7% on average in the 120 days before the announcement. [4] A buyer on announcement day entered after a large share of that gain.
Correction two: large firms barely move
The Hwang medians for seven large firms sit near 1% to 2% in size. [3] A holder of a diversified large-cap drug maker should not expect an approval to change the share price in a visible way.
Correction three: the same move can reverse
Biogen rose 58% at midday on approval day. [8] The company ended Aduhelm development and sales on January 31, 2024. [9] A one-day gain is a statement about expectations on that day.
Correction four: exclusivity is finite and dated
Average market exclusivity runs about 12 to 14 years. [14] Humira revenue fell 37.6% in 2024 after the 2023 loss of exclusivity. [18][20] Any valuation that assumes a drug earns forever is wrong by construction.
Checklist: How to Judge a Claim About Drug Stock Reactions
Use these questions on any article, report or sales deck that cites a price reaction.
Does the claim say which window it used?
Hwang reports five windows from one source, and the size ratio between negative and positive moves ranges from 0.8 to 4.3 across them (derived). [3] A claim without a window cannot be checked.
Does the claim say whether the figure is intraday or closing?
The Biogen 58% figure is a midday move. [8] The Amarin 67% figure is a share-price drop reported after the ruling. [6] Neither is a cumulative abnormal return.
Does the claim use an average or a median?
Hwang reports medians. [3] The settlement studies report averages. [1][2] Averages in a small sample move with one large event, and medians do not.
Does the claim say how many events it covers?
The samples above range from 24 events to 400. [3][19] A result from 8 negative events is a direction, not a rate. [3]
Does the claim say who paid for the study?
The 2024 settlement paper discloses funding from the Blue Cross Blue Shield Association. [2] Funding does not invalidate a result, but a reader should know it.
Does the claim separate the legal event from the stock event?
A ruling date, a Federal Circuit date and a launch date are three events. The Amarin case had a district court ruling, a generic approval in May 2020 and an appeals decision about five months after the ruling. [6][7] A price reaction belongs to one of them, not all three.
Scenario Model: Pricing a Litigation Event Against an Approval Event
This section combines the reported effect sizes into one illustration. Every input is an assumption stated in the text. The output is not a forecast for any company.
What assumptions does the model use?
Assume a brand firm with a $50 billion market capitalization. Assume it announces a settlement that the market reads as delaying generic entry. We apply the 3.5% average from the 2014 to 2023 sample. [2] We apply the 6% average from the earlier sample as an upper case. [1]
What does the model produce?
The settlement case adds $1.75 billion at 3.5% and $3.00 billion at 6% (derived). Now compare a trial result for the same firm. Hwang reports a median of +0.8% for positive news in the window from two days before to the event day. [3] On $50 billion, that is $0.40 billion (derived). The negative-news median of -2.0% on the same base is a loss of $1.00 billion (derived). [3]
Event
Reported effect
Value change (derived)
Source
Potentially collusive settlement, average
+3.5%
+$1.75 billion
[2]
Reverse-payment settlement, average
+6%
+$3.00 billion
[1]
Positive trial result, median
+0.8%
+$0.40 billion
[3]
Negative trial result, median
-2.0%
-$1.00 billion
[3]
What does the comparison show?
On this assumed base, the settlement averages are 4.4 to 7.5 times the positive trial median (derived: 3.5 divided by 0.8, and 6 divided by 0.8). The two numbers come from different samples, different periods and different event types. We use the ratio only to show the order of magnitude.
What does the model leave out?
It leaves out the commercial clock. An event that adds 3.5% to a share price today can still be followed by a revenue decline when exclusivity ends, as the Humira figures show. [20] It also leaves out firm size effects, because the studies do not report them by market capitalization. [3]
The Four Clocks Framework (Original Classification)
This framework is our own. It is not an industry standard. It sorts the events above by the clock that drives them.
The regulatory clock
It starts at approval and runs on FDA exclusivities: 5, 3 and 7 years, plus 6 months for pediatric work. [10] Biologics run on 12 years. [14]
The patent clock
It starts at filing and runs 20 years, with extension limited to 5 years and a 14-year post-approval cap. [10][11]
The litigation clock
It starts at the Paragraph IV notice and runs on 45-day and 30-month deadlines. [12] This clock produces the largest single-day moves in our evidence. [5][6]
The commercial clock
It starts at launch and depends on uptake, coverage and competition. Aduhelm shows that this clock can stop even when the other three run. [8][9]
Event types by clock (original classification)
Event type
Examples
Typical pricing pattern
Evidence
A. Scheduled binary events
FDA action dates, trial readouts
Partly priced in before the date
[3][4][19]
B. Unscheduled legal rulings
District court Paragraph IV decisions
Large single-day moves possible
[5][6][7]
C. Negotiated outcomes
Brand-generic settlements
Moves only when the deal delays entry
[1][2]
D. Slow-burn exposure
Loss-of-exclusivity dates
Dated years ahead; effect appears in results
[18]
What Does This Mean for Brand Manufacturers, Generic Developers and Analysts?
What this means for brand manufacturers
A patent ruling can cost more than an approval adds. Amarin lost 67% on one ruling, while median large-firm trial moves stayed near 1% to 2%. [3][6] A brand firm with one key product has the most exposure to the litigation clock.
What this means for generic entry
Generic entry depends on court outcomes and on supply. Hikma had FDA approval in May 2020, and Amarin argued that generic makers might lack large supplies. [7] Approval and launch are separate events.
What this means for biosimilars
Biologics have a statutory 12-year reference product period, split into 4 years and 8 years. [14] Humira biosimilars reached the U.S. market after the 2023 loss of exclusivity. [18]
What this means for analysts who track patent and exclusivity dates
DrugPatentWatch lists U.S. patent expirations by year, Paragraph IV challenges, 180-day exclusivity, new chemical entity exclusivity expirations, tentative approvals and authorized generics. [17] An analyst can use those fields to build an event calendar. The calendar should then be checked against the Orange Book, court dockets and company filings before any model uses it.
Key Takeaways
Brand stock prices rose about 6% on average at announcement of settlements with a reverse payment, across 68 settlements since 1993. [1]
The 17 potentially collusive settlements from 2014 to 2023 raised brand stock prices by about 3.5% on average. [2]
Median trial-result moves at seven large firms were about 1% to 2%, and negative news moved prices more in four of five windows (derived). [3]
Stocks of companies with positive phase III oncology trials rose 13.7% on average in the 120 days before the announcement. [4]
FDA decisions showed no pre-decision price difference between positive and negative outcomes in the oncology sample. [4]
Amarin fell 67% after the Nevada ruling, and the Federal Circuit affirmed it on September 3, 2020. [6][7]
Biogen rose 58% at midday on Aduhelm approval and ended development and sales on January 31, 2024. [8][9]
Market exclusivity averages about 12 to 14 years, and patent term extension is limited to 5 years and 14 years after approval. [11][14]
FAQ
How much should I expect a stock to move on FDA approval?
There is no single number. Large-firm trial news moved prices by about 1% to 2% at the median. [3] Smaller or less diversified firms can move much more, as Biogen’s 58% midday jump showed. [8] Use company size and product concentration as your first filters.
Does a patent grant move a drug stock?
Kogan and co-authors used stock market reactions to patent news to value patents issued to U.S. firms from 1926 to 2010. [16] We did not verify a drug-specific figure, so we do not give one.
Which moves a stock more, a court ruling or an approval?
In the cases we verified, the court ruling moved more: Amarin fell 67%. [6] The evidence is two selected cases, not a systematic comparison.
Why do reverse-payment settlements raise brand stock prices?
The authors read the rise as the market’s estimate of expected profit from delayed generic entry. [1][2]
How long can a Paragraph IV challenge block generic approval?
An automatic stay lasts 30 months from receipt of the notice, if the brand sues within 45 days. [12]
What is the longest a patent can run after FDA approval?
Fourteen years after approval is the cap on the combined remaining term and extension. [11]
How long does orphan drug exclusivity last?
Seven years, against 5 years for a new chemical entity. [10]
Can generics enter before a patent expires?
Yes. Paragraph IV decisions determine whether a generic firm can enter before exclusivity ends. [5] The Vascepa rulings are an example. [7]
How do I build a patent-event calendar?
Start with expiration, Paragraph IV and exclusivity fields in a tool such as DrugPatentWatch. [17] Confirm each date against primary records.
Why is it hard to run clean event studies on approvals?
The count is small. CDER approved 46 novel drugs in 2025, about one every 5.4 trading days (derived). [15] Overlapping news at the same firm then contaminates the window.
References
Drake, K. M., Starr, M. A., & McGuire, T. G. (2014). Do “reverse payment” settlements of brand-generic patent disputes in the pharmaceutical industry constitute an anticompetitive pay for delay? (NBER Working Paper No. 20292). National Bureau of Economic Research. https://nber.org/papers/w20292
Drake, K. M., & McGuire, T. G. (2024; rev. 2025). Using stock price movements to estimate the harm from collusive drug patent litigation settlements (NBER Working Paper No. 33196). National Bureau of Economic Research. Later published in the Journal of Health Economics, 103 (2025). https://www.nber.org/papers/w33196
Hwang, T. J. (2013). Stock market returns and clinical trial results of investigational compounds: An event study analysis of large biopharmaceutical companies. PLoS ONE, 8(8), e71966. https://pmc.ncbi.nlm.nih.gov/articles/PMC3737210
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