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CO-91 Denial Code: Dispensing Fee Adjustment

CO-91 means the payer reduced or changed the dispensing fee on a pharmacy claim, typically to the fee set in the pharmacy contract. Under the CO group, the difference is a contractual adjustment the pharmacy absorbs.

Quick facts

Code
CO-91 (CARC 91)
Status
Active In use since January 1, 1995.
Code set
Claim Adjustment Reason Codes (CARC)
Group codes
  • CO (Contractual Obligation): The dispensing fee difference is a contractual write-off for the pharmacy or dispensing provider and cannot be billed to the patient.
Official description
Dispensing fee adjustment.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What CO-91 means

CARC 91 is a dispensing fee adjustment. Pharmacy claims are paid as an ingredient cost plus a dispensing fee that compensates the pharmacy for filling the prescription. When the payer pays a fee different from the one submitted, it reports the difference with CARC 91.

In most cases the pharmacy submitted its standard fee and the payer paid the fee in its network contract. The difference is a contractual adjustment, which is why the typical group is CO.

Example: a pharmacy submits a dispensing fee higher than its contract with a plan allows. The payer pays the contracted fee, and the gap shows as CO-91. The ingredient cost may carry its own adjustment under CO-90 on the same claim.

Common causes

  • The submitted dispensing fee exceeds the contracted fee for that plan or network.
  • Different fees apply by claim type (for example, brand versus generic, or retail versus long-term care), and the payer applied a lower tier.
  • Multiple fills in a short period triggered a plan rule that limits dispensing fees per period.
  • Compound or specialty claims were paid with a standard fee rather than an enhanced one.
  • The payer’s contract setup for the pharmacy’s NCPDP or NPI identifier is out of date.

How to fix it

  1. Look up the contracted dispensing fee for the plan, network, and claim type on the fill date.
  2. If the payment matches, post CO-91 as a contractual adjustment. The patient does not owe it.
  3. If the payment is lower, contact the payer or PBM help desk and request reprocessing, following its pricing dispute process.
  4. Check claim fields such as days supply, compound indicator, and submission clarification codes. Errors there can change the fee tier. Reverse and rebill if the claim data was wrong.
  5. Escalate recurring shortfalls to your contracting team or pharmacy services administrative organization, if you use one.

How to prevent problems with CO-91

  • Load each plan’s dispensing fee schedule into your pharmacy system so expected reimbursement is calculated at adjudication.
  • Verify network and contract enrollment when a pharmacy changes ownership, location, or identifiers.
  • Monitor paid dispensing fees by plan. A sudden drop can point to a contract amendment or setup error.
  • Review pharmacy adjustments separately from true rejections. For a structured way to read remittance codes, see how to read CARC and RARC codes.
  • CO-90 (Ingredient cost adjustment.): The adjustment to the drug ingredient cost, the other half of pharmacy pricing.
  • CO-262 (Adjustment for delivery cost.): Pharmacy delivery cost adjustment, reported separately from the dispensing fee.
  • CO-266 (Adjustment for compound preparation cost.): Compound preparation cost adjustment for compounded prescriptions.
  • CO-205 (Pharmacy discount card processing fee): Pharmacy discount card processing fee, a different pharmacy fee.

CO-91 FAQ

Is a CO-91 adjustment normal?

Usually. Pharmacies often submit a dispensing fee higher than the contracted fee, and the payer reduces it. It is worth disputing only when the paid fee is lower than your contract.

Why was the dispensing fee reduced to zero?

Some contracts fold the dispensing fee into the ingredient price or pay no separate fee for certain claim types. Check your contract and the payer's pharmacy manual for that plan.

Can a medical office see CO-91?

It is primarily a pharmacy code. Medical claims for drugs usually do not carry a dispensing fee, so CARC 91 on a medical claim is uncommon.