Medicare Advantage — also called Medicare Part C — has become the dominant way Americans receive their Medicare benefits. More than half of all Medicare beneficiaries are now enrolled in a Medicare Advantage plan, drawn in by $0 premiums, dental and vision add-ons, and the simplicity of a single card. But the marketing rarely leads with the trade-offs. Before you sign up during the Annual Enrollment Period (October 15 through December 7) or switch plans during the Open Enrollment Period (January 1 through March 31), you need a clear-eyed look at what Medicare Advantage takes away — not just what it adds.
The first and most consequential disadvantage is network restriction. Original Medicare — Parts A and B — is accepted by roughly 93% of non-pediatric primary care physicians across the country, according to Medicare.gov. You can walk into virtually any hospital, specialist's office, or outpatient clinic that accepts Medicare and receive covered care. Medicare Advantage works differently. Most plans are either Health Maintenance Organizations (HMOs) or Preferred Provider Organizations (PPOs). HMO plans typically require you to stay within a defined network of doctors and hospitals, and you usually need a referral from a primary care physician before seeing a specialist. PPO plans offer more flexibility but charge significantly higher cost-sharing when you go out of network. If your cardiologist, oncologist, or long-time internist isn't in your plan's network, you may face the choice of paying full price or switching providers entirely.
Network adequacy is not uniform across the country. In rural areas, Medicare Advantage networks can be thin — sometimes covering only one or two hospitals within a reasonable driving distance. If you travel frequently, spend winters in Florida and summers in Maine, or have family in another state where you might need care, a network-based plan creates real logistical problems. Original Medicare, by contrast, covers you anywhere in the United States where Medicare is accepted, with no referrals required and no network boundaries to navigate.
The second major disadvantage is prior authorization. Medicare Advantage plans are run by private insurance companies — Humana, UnitedHealthcare, Aetna, Blue Cross Blue Shield, and others — and those companies have the legal right to require prior authorization before approving certain services, procedures, medications, and even hospital stays. This means your doctor may recommend a procedure, but the insurance company can delay or deny it pending a review. A 2022 report from the HHS Office of Inspector General found that Medicare Advantage plans denied 13% of prior authorization requests for services that met Medicare coverage rules — meaning care that Original Medicare would have covered was being blocked. While the denial rate has drawn congressional scrutiny and new CMS rules have tightened the timeline for authorization decisions, prior authorization remains a structural feature of Medicare Advantage that does not exist in Original Medicare.
Third, consider the out-of-pocket cost ceiling — and how high it actually is. Medicare Advantage plans are required by law to cap your annual out-of-pocket costs, which sounds like a safety net. But in 2025, CMS set the maximum allowable out-of-pocket limit at $9,350 for in-network services. Plans that include out-of-network coverage can set combined limits as high as $14,000. Compare that to Original Medicare, which has no out-of-pocket cap — but which pairs naturally with a Medigap (Medicare Supplement) policy that can cover most or all of your cost-sharing. A Medigap Plan G, for example, covers the Part A deductible, skilled nursing facility coinsurance, and all Part B coinsurance after you pay the annual Part B deductible ($257 in 2025). For someone with serious health needs, a Medigap policy plus Original Medicare may produce lower total annual costs than a Medicare Advantage plan with a $9,000 out-of-pocket exposure.
Fourth, Medicare Advantage plans change every single year. The insurance company can alter premiums, copayments, deductibles, drug formularies, provider networks, and covered benefits from one January 1 to the next. A plan that worked well for you in 2024 may have dropped your specialist, raised your drug copay, or changed its star rating by 2025. This annual variability requires you to actively review your plan every fall during the Annual Enrollment Period — comparing your current plan against alternatives on Medicare.gov's Plan Finder tool. Many beneficiaries don't do this review and end up paying more or losing access to providers they depend on. Original Medicare's core benefits, by contrast, are set by federal law and don't shift year to year.
Fifth, if you enroll in Medicare Advantage and later want to switch back to Original Medicare with a Medigap policy, you may face a significant barrier: medical underwriting. In most states, Medigap insurers can review your health history and charge you higher premiums — or deny you coverage entirely — if you apply outside of a guaranteed issue window. Your guaranteed issue right is strongest when you first turn 65 and enroll in Medicare Part B. If you spend several years in a Medicare Advantage plan and then develop a chronic condition like diabetes, heart disease, or cancer, switching back to Original Medicare with comprehensive Medigap coverage may become prohibitively expensive or impossible in states without additional protections. Thirteen states — including California, New York, Oregon, and Illinois — have birthday rules or year-round guaranteed issue laws that give beneficiaries more flexibility, but residents of the remaining 37 states face real lock-in risk once they've been in Medicare Advantage for a few years.
Sixth, Medicare Advantage drug coverage — Part D — is bundled into most plans, which sounds convenient but creates complications. The formulary (the list of covered drugs) varies by plan and can change annually. A medication you've taken for years may be moved to a higher cost tier, require step therapy (where you must try a cheaper drug first), or be dropped from coverage entirely. With Original Medicare, you choose a standalone Part D plan separately, which gives you the ability to shop specifically for the plan that best covers your exact medications at the lowest cost — independent of your medical coverage decisions.
Seventh, and perhaps most underappreciated, is the issue of care coordination and continuity when you're seriously ill. Medicare Advantage plans have financial incentives to manage costs, which can work in your favor for routine care but may create friction when you need expensive, complex treatment. Hospitalizations, rehabilitation stays, home health services, and skilled nursing facility care all require the plan's approval and are subject to coverage limits that may differ from what Original Medicare provides. For example, Original Medicare covers up to 100 days in a skilled nursing facility following a qualifying hospital stay, with coinsurance beginning on day 21. Medicare Advantage plans must cover at least this much, but the specific cost-sharing structure varies by plan — and some plans have imposed stricter criteria for continued coverage that have drawn legal challenges.
Data Snapshot: According to CMS.gov data, there were 7,929 Medicare Advantage plans available nationwide for the 2025 plan year — a figure that reflects the enormous expansion of the market over the past decade. The average Medicare Advantage plan premium in 2025 was approximately $17 per month, according to CMS, though a large share of enrollees are in $0-premium plans. Despite the low premium appeal, CMS data also shows that plan star ratings are widely distributed: in 2025, fewer than 40% of Medicare Advantage enrollees were in plans rated 4 stars or higher — meaning the majority of beneficiaries are in plans that fall below the threshold CMS considers high-performing.
None of this means Medicare Advantage is the wrong choice for everyone. For healthy beneficiaries in their mid-60s who live in urban areas with robust provider networks, who take few or no specialty medications, and who want the simplicity of a single plan with dental and vision coverage, Medicare Advantage can be a cost-effective option. The $0 premium is real money saved each month. The extra benefits — gym memberships, over-the-counter allowances, transportation — have genuine value for some people.
But for beneficiaries with chronic conditions, those who see multiple specialists, anyone who travels frequently or splits time between states, or people who simply want the freedom to see any Medicare-accepting provider without asking permission, Original Medicare paired with a Medigap policy and a standalone Part D plan may offer more predictable, comprehensive coverage — even if the monthly premiums are higher.
The most important step you can take is to compare your specific situation — your doctors, your drugs, your health history, and your financial tolerance for out-of-pocket risk — against the actual plan options available in your ZIP code. Medicare.gov's Plan Finder tool lets you enter your prescriptions and see estimated annual costs side by side. Your State Health Insurance Assistance Program (SHIP) offers free, unbiased counseling from trained volunteers who have no financial stake in which plan you choose. To find your local SHIP counselor, visit shiphelp.org or call 1-800-MEDICARE. These resources exist precisely because the Medicare landscape is complex enough that even well-informed beneficiaries benefit from a second set of eyes before making a decision that affects their health coverage for the next 12 months.