Evergreening is a strategy pharmaceutical companies use to extend their monopoly on a drug beyond the original patent’s 20-year term. Rather than developing something genuinely new, a company patents slight modifications of an existing drug, like a new crystal form, a different dosage, or a minor chemical tweak, to keep generic competitors off the market for years longer. The goal is almost always economic, not therapeutic. As one pharmaceutical policy expert put it: “Typically, when you evergreen something, you are not looking at any significant therapeutic advantage. You are looking at a company’s economic advantage.”
How Evergreening Works
A drug’s original patent covers its core chemical compound, its active ingredient. That patent lasts 20 years from the filing date, and once it expires, generic manufacturers can legally produce cheaper versions. Evergreening disrupts this process. As a patent nears expiration, the brand-name company files new patents on variations of the same drug: a different salt form, a new coating, an extended-release version, a specific crystal structure. Each of these secondary patents can trigger fresh exclusivity periods, pushing back the date when generics can enter the market.
The United Nations has identified 12 categories of secondary pharmaceutical patent claims that companies commonly pursue. These include polymorphs (different physical forms of the same molecule), enantiomers (mirror-image versions of a molecule), salts, esters, new dosages, new medical uses, drug combinations, and metabolites. The company then rolls out the “new” version of the drug, often discontinuing or deprioritizing the original, and shifts patients and prescribers to the reformulated product before generic competition can gain a foothold.
The Most Common Tactics
One of the most widely used strategies is called a chiral switch. Many drug molecules exist as pairs of mirror images, and the original patent may cover the mixture of both. As that patent expires, a company can isolate just one version, patent it separately, and market it as a new drug. Nexium is the textbook example. It contains only half the molecule found in its predecessor Prilosec, earning it the nickname “Half-o’-Prilosec.” Despite this minimal change, Nexium was marketed as a distinct product and generated billions in sales while keeping generics at bay. Other blockbuster chiral-switch drugs include Lexapro (derived from Celexa), Xyzal (from Zyrtec), and Lunesta (from an older sleep aid).
Another common approach is reformulating the drug into an extended-release version. A company takes a pill designed to be taken multiple times a day and creates a once-daily version, patents the new delivery method, and moves patients to it. This is what happened with drugs like Adderall XR and Ritalin. In both cases, the reformulation allowed the manufacturer to maintain market exclusivity well beyond the original compound’s patent life. Companies also patent specific doses for new conditions, as happened when the maker of Cialis patented a low daily dose for a different use than the original on-demand version.
Patent Thickets and the Orange Book
Evergreening becomes especially powerful when companies don’t file just one secondary patent but dozens, creating what’s known as a patent thicket. A competing generic manufacturer must either wait for all relevant patents to expire or challenge them in court, one by one. Both options cost time and money that smaller companies often can’t afford.
The most dramatic example is Humira, the blockbuster anti-inflammatory drug. AbbVie secured over 130 patents around Humira, creating a thicket that kept biosimilar competitors out of the U.S. market from the drug’s launch in 2002 until 2023, seven years past the original patent’s expiration in 2016. That delay cost the healthcare system an estimated $7.6 billion.
In the U.S., brand-name companies list their patents in an FDA database called the Orange Book. When a generic manufacturer wants to bring a competing product to market, it must account for every listed patent. This gives brand-name companies a powerful incentive to list as many patents as possible, even those of questionable relevance. The Federal Trade Commission has been actively pushing back: in 2025, the FTC renewed challenges against more than 200 patent listings it considers improper, targeting brand-name asthma, diabetes, epinephrine autoinjector, and COPD drugs. The agency sent warning letters to companies including Novartis, Teva, and others, arguing that these listings were shielding drugs from generic competition and keeping prices artificially high.
The Cost to Patients and Insurers
The financial impact is enormous. A study published in the Journal of Managed Care & Specialty Pharmacy found that 73 drug ingredients were subject to evergreened reformulations between 2008 and 2016. These reformulations increased Medicaid spending alone by $9.35 billion over that period, representing about 2.5% of total Medicaid outpatient drug expenditures. Extrapolated across all payers, including private insurance and out-of-pocket spending, the figure rises to an estimated $62 billion.
Twelve drugs accounted for 97% of those excess costs. The biggest offenders were ADHD medications and psychiatric drugs: Adderall’s reformulations added $2.68 billion in unnecessary Medicaid costs, Ritalin added $2.13 billion, the antipsychotic Seroquel added $1.75 billion, and Focalin added $1.17 billion. In each case, patients and insurers were paying brand-name prices for drugs whose core compounds had long since lost patent protection.
The Industry’s Defense
Pharmaceutical companies and their legal advocates argue that secondary patents are a legitimate and necessary part of drug development. Bringing a new drug to market is extremely risky, with most candidates failing in clinical trials. Strong patent protection, the argument goes, is what makes companies willing to invest in that gamble at all. If a reformulation genuinely improves how a drug is absorbed, reduces side effects, or makes dosing more convenient, the innovation deserves protection.
There’s also a technical point: not every secondary patent is frivolous. Some reformulations do meaningfully improve a drug’s performance. An extended-release version that a patient takes once instead of three times daily can improve adherence, which translates to better health outcomes. The challenge is distinguishing these real advances from changes made purely to reset the patent clock.
How Different Countries Handle It
The U.S. has historically been permissive about secondary patents, though that’s beginning to shift. Legislation introduced in the 119th Congress, the Stopping Pharma’s Ripoffs and Drug Savings For All Act, would direct the U.S. Patent and Trademark Office to review its procedures to prevent granting multiple patents for the same drug unless they cover genuinely distinct inventions. The bill has been introduced but not yet passed.
India takes the most aggressive stance of any major country. Section 3(d) of India’s Patents Act explicitly blocks patents on new forms of known substances unless the applicant can prove the modification results in enhanced therapeutic efficacy. The landmark case testing this provision was Novartis’s attempt to patent a new crystal form of the leukemia drug Gleevec. India’s Supreme Court rejected the patent, ruling that a 30% increase in bioavailability was not the same as improved therapeutic efficacy. The court stated that therapeutic efficacy “must be judged strictly and narrowly,” meaning that better absorption or shelf stability alone isn’t enough. The modification has to make the drug work better in the body against the disease it treats.
This distinction matters. Under U.S. patent law, nearly any novel feature of a drug can qualify for protection. Under India’s framework, the bar is specifically tied to whether patients get a better treatment. The Indian approach has been controversial internationally, with pharmaceutical companies arguing it discourages investment, but it has also made India a major source of affordable generic medications for low- and middle-income countries worldwide.