CO 211 denial code

Claim adjustment reason code 211. Often reported as CO 211.

NDC not eligible for rebate

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What 211 means

The drug was billed with a National Drug Code that is not eligible for a manufacturer rebate, so the plan does not cover it.

Some programs, Medicaid in particular, pay only for drugs whose manufacturers take part in a rebate agreement. If the NDC on the claim is not on the rebate list, the drug is not covered.

Check the NDC itself first. The wrong package size or an outdated NDC can trigger this even when a covered version of the drug exists.

Group codes seen with 211

On a remittance, 211 comes after a group code. These are the ones it is most often reported with:

• CO 211 (Contractual Obligation): The provider's side of the ledger. The reduction comes from the payer contract or a rule the provider has to follow, and the patient normally cannot be billed for it.

The payer chooses the group code for each adjustment, so the same reason code can appear with another group code on your remittance. Read the two together. More about group codes.

Common causes

• The manufacturer of the drug does not participate in the program's rebate agreement.
• The NDC billed was for a package or labeler different from the one actually used.
• An old or terminated NDC was still in the billing system.

What to do next

1. Verify the NDC on the claim against the vial or package actually given.
2. Check whether the NDC is on the program's rebate eligible list for the date of service.
3. Correct the NDC and resubmit if a covered product was actually used.
4. Work with pharmacy purchasing to stock rebate eligible products where possible.

Related codes

• 16 (reason code) Missing information or billing error
• 204 (reason code) Not covered under the patient's plan
• 96 (reason code) Service not covered by the plan