The Medicaid Drug Rebate Program and generic drugs

State Medicaid programs spent $106.4 billion on outpatient drugs in fiscal 2024 before rebates, and drug manufacturers paid back $58.4 billion, according to a MACPAC tally¹ of federal data. Generic drugs, which fill most Medicaid prescriptions, accounted for 14.0 percent of the gross spending, a companion MACPAC exhibit² shows.

Those rebates flow through the Medicaid Drug Rebate Program, created in 1990 by section 1927 of the Social Security Act. About 780 manufacturers take part, according to Medicaid.gov³. In exchange for a national rebate agreement, a manufacturer's drugs are covered by every state Medicaid program, and the manufacturer pays each state a rebate every quarter on the units that program paid for. The states and the federal government share the money.

Generics have their own formula inside that program, and three changes in federal law have reshaped it since 2010. This explainer lays out the formula, works through CMS's own example, and follows the money through the cap that came off in 2024.

Two formulas, split by approval pathway

Medicaid sorts every drug into a category. A single source drug is sold under a new drug application (NDA) with no therapeutic equivalent. An innovator multiple source drug is sold under an NDA but has generic competition. A noninnovator multiple source drug, called an "N" drug in CMS systems, is everything else with multiple sources, which in practice means generics approved through abbreviated new drug applications. The definitions sit in section 1927(k)(7)⁶, now codified at 42 U.S.C. 1396r-8.

Which pathway a drug took to approval decides the rate. An authorized generic carries no brand name but is sold under the brand's NDA, so it falls into the innovator category.

Rates come from CMS’s unit rebate amount page⁴. AMP is the average manufacturer price, a confidential figure that manufacturers report to CMS each quarter. Best price, the lowest price a brand manufacturer gives most private buyers, plays no part in the generic formula.

Generic rebate percentages have climbed in steps. Under the statute it was 10 percent for rebate periods before 1994, 11 percent from 1994 through 2009, and 13 percent for periods after December 31, 2009, the change made by the Affordable Care Act.

The inflation add-on that arrived in 2017

Brand drugs have always owed an extra rebate when their AMP rises faster than the consumer price index for all urban consumers (CPI-U). Generics did not, until the Bipartisan Budget Act of 2015. Its section 602 extended the add-on to N drugs to rebate periods beginning after the first anniversary of its November 2, 2015 enactment, which made the first quarter of 2017 the starting point. The baseline for older generics is their AMP in the quarter beginning July 1, 2014, adjusted by CPI-U from September 2014. A generic first marketed after April 1, 2013 uses its fifth full quarter on the market as its baseline instead, the statute says⁶.

HHS's Office of Inspector General measured what the old gap had cost. Its December 2015 report⁷, issued six weeks after the law passed, found that generic price increases outpaced the brand inflation factor in 22 percent of the quarterly AMPs it reviewed. Had generics owed the add-on, the OIG calculated, Medicaid would have collected $1.4 billion more in rebates on the top 200 generics from 2005 through 2014, with the yearly figure rising from more than $39 million in 2005 to more than $464 million in 2014.

CMS publishes a worked example⁵ for a hypothetical generic, Product X, that shows how the two pieces add up. The numbers are CMS's, rounded as CMS rounds them.

In this example the manufacturer owes about 44 percent of its AMP back to Medicaid, more than three times the 13 percent basic rate, because its price rose 46 percent from the baseline while CPI-U rose less than 1 percent. The inflation piece does the work when a generic's price climbs, which happened to many products during the 2013 to 2015 price spikes. Price rises remain the exception. Only three of the 47 drugs GxRadar tracks (simvastatin, citalopram and amoxicillin) cost pharmacies more in October 2026 than five years earlier, according to our analysis of CMS NADAC files¹⁰. NADAC measures pharmacy acquisition cost, which is a different number from AMP.

The cap came off in 2024

From 2010 through 2023, a drug's total Medicaid rebate could not exceed 100 percent of its AMP. The American Rescue Plan Act of 2021 (section 9816) ended that limit for rebate periods beginning January 1, 2024, by adding an end date to the cap in section 1927(c)(2)(D)⁶. The generic formula borrows that same provision by cross-reference, so the cap ended for N drugs on the same date.

Lifting the cap mattered most for drugs whose prices had risen for years. KFF reported⁸ that a MACPAC analysis found 4.7 percent of drugs hit the cap in fiscal 2020, and that the Congressional Budget Office projected the repeal would reduce federal spending by more than $17 billion over 10 years. KFF also described manufacturers responding before the deadline by cutting list prices on some brands and replacing other brand products with lower-priced generic versions.

That response matters for generic users. When a brand is withdrawn and its maker sells a generic version instead, the preferred drug lists that states use can shift, and KFF noted that some states changed prior authorization rules for an inhaler in exactly that situation.

Classification fights and the 2024 rule

Because a brand pays at least 23.1 percent and a generic 13 percent, the category a manufacturer reports carries real money. The Medicaid Services Investment and Accountability Act of 2019 gave CMS new authority over misclassified drugs, and CMS implemented it in a final rule published September 26, 2024⁹, effective November 19, 2024. The statute now lets CMS correct a misclassification itself, suspend the drug from the rebate agreement, or impose a civil money penalty for each quarter of up to 23.1 percent of AMP on every unit Medicaid paid for.

How rebates fit with what Medicaid pays pharmacies

Rebates arrive after the fact. When a pharmacy fills a Medicaid prescription, the state pays it based on an ingredient cost benchmark such as NADAC or the federal upper limit, plus a dispensing fee. Months later the manufacturer pays the state a rebate on the same units. Our pieces on how Medicaid pays for generics and how state programs set those payments cover the first half of that exchange.

A rebate agreement also ties manufacturers to other federal programs. To have its drugs covered by Medicaid, a manufacturer must also sign a pricing agreement for the 340B program and a master agreement with the Department of Veterans Affairs for the Federal Supply Schedule, Medicaid.gov³ says.

The fiscal 2024 MACPAC rebate total includes state supplemental rebates and reflects timing lags, since rebates collected in one quarter generally pay for drugs dispensed earlier. MACPAC's notes say spending and rebate dollars for a given period are not necessarily aligned.

Medicare's new inflation rebates may shrink Medicaid's over time. KFF pointed out⁸ that if the Inflation Reduction Act slows drug price growth, Medicaid will collect less in inflation-based rebates. GxRadar's explainer on Medicare inflation rebates covers how that newer program treats generics.