How to Spot a Bad Medicare Part D Plan Before You're Stuck With It

Every year during Open Enrollment, millions of Medicare beneficiaries pick a Part D prescription drug plan based on the wrong criteria — usually the premium. The result is that many of them end up spending hundreds or thousands of dollars more than they needed to, on medications they could have gotten far more cheaply through a better-matched plan.

There is no single list of "the 10 worst Part D plans" that applies to everyone, because the "worst" plan for your parent is specifically the one that does not cover their drugs at a reasonable tier, or has a high deductible they will hit every year, or charges $8 more than average at the pharmacy they actually use. What makes a Part D plan bad is misalignment with the specific person enrolled in it.

That said, there are consistent patterns, features, and red flags that signal a plan is likely to cost more than it should. Here is what to look for.

The Core Problem: Premium-First Thinking

The most common mistake families make when picking Part D plans is choosing the plan with the lowest monthly premium. This feels logical — premiums are visible, predictable costs. But in Part D, the premium is often the least important variable.

A plan with a $5/month premium might charge your parent $80/month for a drug that costs $10/month under a plan with a $35 premium. After three months, your parent is already behind.

The only number that matters is Total Annual Drug Cost — the combination of premiums, deductible, and actual drug copays or coinsurance for your parent's specific medication list. Medicare.gov's Plan Finder calculates this automatically when you enter your parent's drugs. If you are not using this number to compare plans, you are not actually comparing plans.

Red Flag 1: Your Parent's Drugs Are Not on the Formulary

Every Part D plan has a formulary — a list of covered drugs. Plans are required to cover at least two drugs in every therapeutic category, but they are not required to cover any specific drug. If your parent takes a medication that is not on a plan's formulary, the plan either will not cover it at all or will require a coverage exception process that is time-consuming and not guaranteed to succeed.

Before your parent enrolls in any plan, confirm that every medication they take is listed in that plan's formulary. Use the Medicare Plan Finder (medicare.gov/plan-compare) — enter each drug by name, dosage, and frequency. The tool will flag which plans cover each drug and at what tier.

If a plan's formulary does not list a drug your parent currently takes, that plan is a bad choice regardless of the premium.

Red Flag 2: Your Parent's Drug Is on a High Tier

Formularies organize drugs into tiers, and the tier determines how much your parent pays per prescription. Typical tier structures:

• Tier 1: Generic drugs — low copay (often $0–$10)
• Tier 2: Preferred brand-name drugs — moderate copay ($15–$40)
• Tier 3: Non-preferred brand drugs — higher copay ($40–$80)
• Tier 4: Specialty drugs — typically 25–33% coinsurance, which can be hundreds of dollars

The same drug can be on Tier 2 in one plan and Tier 3 in another — meaning the premium-adjusted total cost differs significantly between plans, even for the same drug. This is not random. Plans structure tiers based on contracts with drug manufacturers, and those contracts change each year during Open Enrollment.

This is why you must compare plans every single year during the Annual Open Enrollment Period (October 15 – December 7). A plan that was the cheapest option in 2025 may have moved your parent's drug to a higher tier for 2026.

Red Flag 3: The Deductible Is High and Your Parent Will Definitely Hit It

The standard Part D deductible in 2026 is $590. Plans can charge up to this amount as an annual deductible before coverage kicks in, or they can waive it entirely for certain tiers (many plans waive the deductible on Tier 1 and Tier 2 drugs).

A plan with a high deductible and a low premium is often a trap for parents who take multiple regular medications. If your parent pays $590 in January before their drug coverage even starts, that deductible effectively needs to be added back into the annual cost comparison.

Plans that have no deductible for the tiers where your parent's drugs sit are generally preferable, even if the monthly premium is slightly higher. Run the total cost calculation rather than looking at deductible and premium in isolation.

Red Flag 4: The Pharmacy Network Is Inconvenient or Restrictive

Not all pharmacies are treated equally within a Part D plan. Plans designate certain pharmacies as "preferred," and drugs purchased at preferred pharmacies cost less than the same drugs at "standard" network pharmacies.

If your parent has a lifelong relationship with a neighborhood pharmacy that is not in a plan's preferred network, they will pay more every time they fill a prescription. Over the course of a year, this can add up to hundreds of dollars.

When comparing plans in the Medicare Plan Finder, select your parent's actual pharmacy — the one they actually use — along with a major chain and a mail-order option. The cost comparison will reflect real-world pricing at each pharmacy type. Mail-order is often significantly cheaper for maintenance medications (drugs your parent takes every month for a chronic condition), and most Part D plans offer mail-order delivery as a preferred option.

Red Flag 5: The Plan Has Low Star Ratings for Drug Plan Performance

CMS rates Part D plans on a 1-to-5 star scale based on quality and customer service metrics, including:

• Getting needed drugs
• Safety and accuracy of drug pricing
• Customer service and complaint rates
• Member experience ratings

Plans with 2.5 stars or below have measurable service problems. These include chronic prior authorization delays, high rates of member complaints, errors in billing, and difficulty reaching customer service. In a year when your parent needs a prior authorization approved quickly — which happens with certain specialty drugs and some medical equipment — a poorly rated plan's bureaucratic failures can become a real health issue.

Check the star rating for every plan you are considering. The Medicare Plan Finder displays it. Filtering for 4-star and above plans is a reasonable starting screen.

Red Flag 6: The Plan Has a History of Significant Formulary Changes

Formularies change every year. A plan can add, remove, or reprice any drug from one year to the next. Plans that make dramatic formulary changes year over year — dropping commonly used drugs, shifting popular medications to higher tiers — are higher-risk for your parent's long-term cost stability.

During Open Enrollment, CMS requires all Part D plans to send their enrollees an Annual Notice of Change (ANOC), which details what is changing for the upcoming plan year. If your parent receives one of these notices and the cost of a drug they take regularly is going up substantially, that is a strong signal to shop for a new plan.

If your parent has been on the same Part D plan for multiple years without shopping during Open Enrollment, there is a good chance they are paying more than necessary. The landscape changes significantly every year.

Red Flag 7: Ignoring the New $2,100 Out-of-Pocket Cap

Starting in 2025, no Medicare beneficiary pays more than $2,000 out of pocket annually for covered Part D drugs. In 2026, this cap rises to $2,100. This is a major protection introduced by the Inflation Reduction Act, and it renders some older cost-comparison strategies obsolete.

For parents with expensive specialty medications (cancer drugs, certain biologics, MS medications), this cap is the most important feature. Previously, these parents could face catastrophic uncapped costs. Now they cannot exceed $2,100 per year regardless of what their drugs cost.

This means that for high-cost drug users, the plan comparison should focus heavily on what tier the expensive medication is on (which affects costs up to the cap) and whether the plan has a convenient pharmacy network. Once the cap is hit in, say, March, the remaining nine months of the year cost nothing out of pocket for drugs.

Plans that appear cheaper on the Plan Finder but place specialty drugs at high coinsurance tiers may actually cost your parent $2,100 faster than a plan with better tier placement — the total is the same, but the cash flow timing matters for parents on fixed incomes.

The Right Way to Compare: Step by Step

Step 1: Go to medicare.gov/plan-compare. Log in to your parent's MyMedicare.gov account if possible — it pulls their claim history and helps populate the drug list accurately.

Step 2: Enter every medication with the correct dosage and frequency. Be precise. "Metformin 500mg twice daily" is priced differently than "Metformin 1000mg once daily."

Step 3: Enter your parent's actual pharmacy, a major chain, and the mail-order option.

Step 4: Sort by "Lowest Drug + Premium Cost" — not by premium alone.

Step 5: Compare the top 3-5 plans on: formulary coverage (all drugs covered?), deductible structure, pharmacy network, and star ratings.

Step 6: Check whether any of the plans are changing their formulary dramatically from the current year by reviewing the ANOC if one has been received.

Do this every year. Open Enrollment runs October 15 – December 7. The best plan for 2025 may not be the best for 2026.

What Happens If Your Parent Is Already in a Bad Plan

If your parent is currently enrolled in a Part D plan that is not serving them well, the Annual Open Enrollment Period (October 15 – December 7) is the time to switch. Changes take effect January 1 of the following year.

If they missed Open Enrollment, the Medicare Advantage Open Enrollment Period (January 1 – March 31) allows switching between Advantage plans that include drug coverage, but does not allow switching stand-alone Part D plans.

Special Enrollment Periods exist for certain life events — moving, losing other coverage, qualifying for Extra Help — that allow changes outside the standard windows.

Our Medicare Enrollment Guide walks through the complete Part D comparison process in detail, including how to read a formulary, what to do if a drug is not covered, how to appeal a coverage denial for a medication your parent needs, and how the Extra Help (Low Income Subsidy) program can dramatically reduce Part D costs for eligible seniors. If your parent's drug plan is costing more than it should, the guide gives you the framework to fix it.