Published October 8, 2026
How often is NADAC updated? Every Tuesday, CMS posts a fresh National Average Drug Acquisition Cost file to its Medicaid site, a rhythm it has kept since 2013. If you check it every week the way the pricing researchers at 46brooklyn do, you will notice something odd: most weeks, barely anything moves. A WAC adjustment here, a brand price tweak there. Then one week a month, the whole file lights up. Thousands of generic drug prices change at once. That week has a name in the pharmacy pricing world: survey results week.
How often is NADAC updated: the two-tier schedule
NADAC is built on a monthly survey. CMS surveys a random sample of retail pharmacies each month about the actual invoice prices they paid for drugs, then averages those into the national file. The weekly Tuesday post is the delivery vehicle; the monthly survey is the engine. Most Tuesday updates only pick up brand-name price changes, which usually follow manufacturer WAC increases, and the occasional correction. The generic prices, the ones that move, wait for the survey cycle.
Survey results week normally lands in the third or fourth week of the month. That is when CMS publishes the price changes derived from the prior month's invoices, and it is almost entirely a generic drug event. Thousands of NDCs get new numbers in one file drop. If you track a specific generic and its NADAC has been flat for weeks, this is the week to watch.
Why one Tuesday can move a price 98 percent
Generic drug prices are volatile in a way brand prices are not. A new generic manufacturer enters, a shortage resolves, a wholesaler contract flips, and the invoice price collapses or spikes in a matter of weeks. Because NADAC averages real invoices, the monthly survey eventually catches all of it at once. The classic example the 46brooklyn researchers keep citing: generic sildenafil 25mg fell from $27 a tablet to $0.56 a tablet in a single monthly update, a 98 percent drop, while brand Viagra sat untouched at around $65 a tablet.
That lag cuts both ways, and this is where I get ambivalent about the schedule. A weekly file built on a monthly survey is the most transparent drug pricing data the public has, and it is free, which matters. But it is not real time. If a generic's price crashed two weeks ago, this Tuesday's file may still show the old number, because the survey that captured the crash has not published yet. Anyone using NADAC to judge whether a pharmacy's price is fair should know they are looking at a photograph, not a live feed. Check the most recent survey results week, not just the most recent Tuesday.
What the Tuesday file actually contains
Each weekly file lists NADAC per unit by NDC, the 11-digit code that identifies the exact drug, strength, and package. Brand prices update when manufacturers change WAC or AWP, which clusters in January and July, the industry's two big price-increase seasons. Drug compendia like First Databank and Medi-Span pull the weekly file into their own pricing modules, and state Medicaid programs and PBM claim systems load the updates into their reimbursement engines, usually within days. That is why the Tuesday rhythm matters beyond researchers: it is the number behind a large share of Medicaid pharmacy reimbursement in the country.
How to use the schedule
If you are a patient checking whether your pharmacy's cash price is reasonable, compare against the latest file but remember the lag: a generic that just dropped in the real world may still show the old NADAC. If you are a pharmacy or a researcher, the workflow is simpler. Watch every Tuesday for brand movements, and mark the survey results week on your calendar, because that is when your generic acquisition costs actually reset. CMS also publishes a NADAC Comparison Database that lets you sort any week's updates by percent change, which is the fastest way to spot the big movers without scrolling thousands of rows.
Frequently asked questions
How often is NADAC updated?
CMS posts NADAC updates every Tuesday. Most weeks bring only small changes, but one week a month, normally the third or fourth, is survey results week, when CMS publishes price changes for thousands of generic drugs based on the prior month's pharmacy invoice survey.
What is survey results week for NADAC?
Once a month, CMS publishes the results of its survey of pharmacy invoice prices from the previous month, updating NADAC for thousands of generic NDCs at once. It is the one week each month when generic drug prices move significantly.
Why did my drug's NADAC price suddenly drop?
Most likely it was survey results week. When the monthly pharmacy survey shows a drug's invoice costs fell, NADAC is revised to match, sometimes dramatically. Generic sildenafil once fell 98% in a single monthly update.
Is NADAC real-time pricing?
No. NADAC reflects invoice prices from a monthly survey, published weekly, so fast-moving generic prices can lag the market by several weeks. For the freshest view, check the most recent survey results week rather than a quiet in-between week.
See the real numbers: look up what pharmacies actually paid for your prescriptions in the NADAC Drug Price Lookup.
Want more of these? I write one practical guide a week on money, health costs, and the tools that decode them. Subscribe free here.