Medicare Advantage vs. Original Medicare for Specialty Drugs: What Nobody Tells You

Medicare has two tracks. Understanding the difference between them — specifically for specialty drugs — could determine whether your next infusion gets approved or denied.

Original Medicare, the federal program created in 1965, is divided into Part A (hospital care) and Part B (outpatient and physician services). Part D, added in 2006, covers prescription drugs. These parts operate under standardized rules set by the Centers for Medicare and Medicaid Services and applied uniformly across the country.

Medicare Advantage, also called Part C, is something different. It is private insurance. Insurance companies contract with CMS to deliver Medicare benefits, receive a fixed monthly payment per enrollee, and are permitted to design their own networks, formularies, and prior authorization policies within CMS guidelines. As of 2024, more than 33 million Medicare beneficiaries were enrolled in Medicare Advantage plans, representing roughly 54 percent of the total Medicare population, according to KFF.¹

The plan you choose affects nearly everything about how your specialty drugs are covered, reviewed, and approved.

Two Systems, Two Drug Categories

To understand the coverage difference, you first need to understand how Medicare categorizes drugs.

Part B drugs are medications administered in a clinical setting: infusions, injections given in a physician's office, and drugs that require clinical supervision. IVIG, chemotherapy, injectable biologics, and physician-administered monoclonal antibodies fall into Part B. These drugs are typically billed by your doctor or infusion center directly to Medicare.

Part D drugs are medications you pick up at a pharmacy or receive by mail to self-administer at home. Many oral specialty drugs, self-injected biologics, and newer oral cancer medications fall into Part D.

Under Original Medicare, Part B drugs have relatively limited prior authorization requirements. CMS sets coverage criteria, and a physician's order combined with documentation that the drug is medically necessary is often sufficient. There is no private insurance company in the middle making a separate coverage determination.

Under Medicare Advantage, this changes substantially. MA plans cover both Part B and Part D drugs, but they are permitted to impose their own formularies and their own prior authorization requirements on top of Medicare's baseline coverage rules. For specialty drugs especially, that additional layer can be significant.

What the Data Shows

The Office of Inspector General published a landmark audit in 2022 examining how Medicare Advantage plans use prior authorization. The findings were direct: MA organizations denied 13 percent of prior authorization requests that auditors determined met Medicare coverage criteria and should have been approved.² In other words, roughly one in eight denials was a denial of care that Original Medicare would have covered.

The OIG also found that MA plans often cited broad criteria such as "not medically necessary" without adequate clinical review documentation, and that many of those denials were overturned on appeal, suggesting the initial denial was not well-founded.

CMS has responded with prior authorization reform rules. A 2024 CMS final rule requires MA plans to maintain prior authorization policies that are no more restrictive than Original Medicare's national coverage determinations for certain items and services. Implementation is ongoing, and enforcement varies.

How Specialty Drug Denials Happen in Medicare Advantage

Several patterns appear frequently when specialty drugs are denied under MA plans.

Step therapy requirements, sometimes called fail-first protocols, require you to try and fail on a less expensive drug before the plan will approve the one your physician prescribed. In some cases, physicians have already determined based on clinical factors that the step drug is inappropriate. The prior authorization process does not always accommodate that determination easily.

Site-of-care restrictions direct where you may receive infusion therapy. An MA plan may require that a drug be administered at an outpatient facility it approves rather than at a hospital outpatient department or specialized infusion center, even when your physician recommends a specific site for clinical reasons.

Quantity limits set maximum dosing thresholds that may not match your physician's prescribed dose. For weight-based biologics or complex dosing regimens, this can result in denials even when the prescription is clinically correct.

Non-formulary status means a drug your physician prescribed is not on the plan's approved drug list at all. You may be able to request a formulary exception, but that process requires documentation and a physician's supporting statement.

Appeal Rights Under Medicare Advantage

Under Original Medicare, disputes over Part B drug coverage typically go through a claims appeals process administered by the Medicare Administrative Contractor for your region.

Under Medicare Advantage, you have access to a five-level appeal process, and the timelines are specific.

The first level is an internal reconsideration by the MA plan itself. For standard appeals, the plan has 60 days to respond. For expedited appeals, where your health would be seriously jeopardized by a standard timeframe, the plan must respond within 72 hours.

If the plan upholds its denial, your appeal moves to the Independent Review Entity, a CMS-contracted independent organization that reviews MA plan denials. The IRE is outside the plan's control and is required to make its own clinical determination.

If you disagree with the IRE's decision and the amount in question exceeds a threshold set annually by CMS, you may request a hearing before an Administrative Law Judge at the Office of Medicare Hearings and Appeals. Beyond that, review is available through the Medicare Appeals Council, and ultimately through Federal District Court.

According to the OIG, most beneficiaries who appeal MA prior authorization denials do not complete the full appeals process. The process is designed for completion; the documentation at each step builds your record.

What to Look For Before Enrolling

If you take specialty drugs and are considering Medicare Advantage, the plan's formulary and prior authorization policies are the most important documents to review before choosing.

CMS requires MA plans to publish their formularies. Before enrolling in or switching to an MA plan, search for your specific drug on the plan's formulary and note its tier, whether prior authorization is required, whether step therapy applies, and which pharmacies or infusion sites are in network.

The plan's Annual Notice of Change, published each fall before the open enrollment period, will show you what is changing in your current plan. Formulary changes — including drugs being removed or moved to higher cost-sharing tiers — must be disclosed in this document.

Open enrollment for Medicare runs from October 15 through December 7 each year. If you are in an MA plan and find that your specialty drug coverage has materially changed, you may be able to switch plans during this window or use the Medicare Advantage Open Enrollment Period from January 1 through March 31 to return to Original Medicare.

A Note on Switching Back

Returning to Original Medicare from Medicare Advantage is possible, but involves one significant consideration: Medigap.

Medigap plans, which supplement Original Medicare by covering cost-sharing and some additional benefits, may not be available to you on guaranteed-issue terms if you have been in Medicare Advantage for more than 12 months. Depending on the state you live in and your health history, Medigap insurers may be permitted to apply medical underwriting, which could result in higher premiums or denial.

If you are considering switching back to Original Medicare from an MA plan, contact your State Health Insurance Assistance Program, known as SHIP, before making the change. This service is free and available in every state. Your SHIP contact information is at shiphelp.org.

The Appeal Window Closes Faster Than You Think

If your MA plan has denied a specialty drug, the timeline for contesting that decision is shorter than most people realize. Standard prior authorization appeals must typically be filed within 60 days of the denial notice. Expedited appeals, for situations where your health is at risk, require you to request that status upfront. Do not wait for the standard timeline if your clinical situation doesn't allow for it.

The documentation you submit at each level of appeal matters. A denial that is poorly supported at the IRE level is harder to reverse at OMHA. If you are preparing an appeal, your physician's clinical documentation and the specific Medicare coverage criteria for your drug are the two most important sources.

¹ KFF. "Medicare Advantage in 2024: Enrollment Update and Key Trends." 2024.

² Office of Inspector General, U.S. Department of Health and Human Services. "Some Medicare Advantage Organization Denials of Prior Authorization Requests Raise Concerns About Beneficiary Access to Medically Necessary Care." April 2022.