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CO-90 Denial Code: Drug Ingredient Cost Adjustment

CO-90 means the payer adjusted the ingredient cost of a drug, usually reducing the submitted cost to the price its contract or pricing benchmark allows. X12 limits this code to pharmaceuticals, so it mainly appears on pharmacy claims.

Code: CO-90 (CARC 90)
Status: Active In use since January 1, 1995; last modified July 1, 2017.
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): The ingredient cost reduction is a contractual adjustment the pharmacy or provider absorbs. It is not billable to the patient.
PR (Patient Responsibility): Rare. Some plans may shift a drug cost difference to the patient, for example under a brand-penalty design. Confirm plan terms before collecting.
Official description: Ingredient cost adjustment. Usage: To be used for pharmaceuticals only.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-90 means

CARC 90 is an ingredient cost adjustment, and its usage note restricts it to pharmaceuticals. Pharmacy reimbursement usually has two parts: the ingredient cost (the drug itself) and a dispensing fee. When the payer or pharmacy benefit manager (PBM) pays less than the submitted ingredient cost, the difference is reported with CARC 90.

Most of the time this is routine. Pharmacies submit their usual and customary price, and the payer pays according to the pricing benchmark and discount written into the contract. The gap is expected, much like CO-45 on a medical claim.

Common causes

The submitted ingredient cost is higher than the contracted pricing formula for that drug.
The payer priced the claim using a maximum allowable cost (MAC) list for a multi-source generic.
The NDC or package size submitted differs from the one the payer priced, which changes the unit cost.
Quantity or days supply was adjusted, reducing the payable ingredient cost.
A pricing file was out of date on either the pharmacy or payer side for the date of fill.

How to fix it

Treat routine CO-90 as a contractual adjustment when the allowed ingredient cost matches your contract pricing for that fill date.
Check the NDC, quantity, and package size on the claim. If they were wrong, correct and reverse and rebill according to the payer’s pharmacy claim process.
If the allowed cost is below contract, gather the pricing terms and the claim detail and submit a pricing inquiry or MAC appeal through the payer or PBM channel. Deadlines and forms vary by PBM.
Do not bill the patient for a CO-90 amount.
Record recurring underpricing by drug so you can raise it during contract review.

How to prevent problems with CO-90

Keep contract pricing terms and MAC appeal procedures accessible to staff who reconcile remittances.
Update drug pricing files regularly so submitted costs and NDCs reflect what is actually dispensed.
Compare paid ingredient cost to acquisition cost by drug. Losses on specific generics are often visible only in aggregate.
Report CO-90 separately from denials. It is a pricing adjustment, not a rejected claim. See how to read CARC and RARC codes.

Specialty notes

Retail, mail-order, and specialty pharmacies see CARC 90 on most paid claims. Physician offices and infusion centers that bill drugs on a medical claim are more likely to see fee schedule or NDC-related adjustments, so a CO-90 on a medical claim is worth confirming with the payer.

CO-91 (Dispensing fee adjustment.): The companion adjustment for the dispensing fee rather than the drug ingredient cost.
CO-45 (Charge exceeds fee schedule/maximum allowable or contracted/legislated fee arrangement.): The general fee schedule reduction used for most medical services.
CO-266 (Adjustment for compound preparation cost.): Adjustment for compound preparation cost, another pharmacy-only component.
CO-295 (Pharmacy Direct/Indirect Remuneration (DIR)): Pharmacy direct and indirect remuneration (DIR), a separate pharmacy fee arrangement.

CO-90 FAQ

Does CO-90 apply to medical claims?

The official usage note says it is for pharmaceuticals only. Medical practices billing office-administered drugs will more often see a fee schedule reduction such as CARC 45.

How do I know if a CO-90 reduction is correct?

Compare the allowed ingredient cost against the pricing terms in your pharmacy contract for that drug, NDC, package size, and fill date. If the allowed cost is lower than the contract, question it with the payer or PBM.

Can the patient be billed for CO-90?

Not when it is reported under CO. That group means the difference is a contractual write-off.

Important: read before using this information

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