Part D began in 2006 as a prescription drug benefit

Medicare Part D launched on January 1, 2006. It was created by the Medicare Modernization Act, passed by Congress in 2003, to help seniors and people with disabilities pay for prescription medications. Before Part D existed, Medicare covered hospital stays and doctor visits, but not the cost of drugs you took at home — a gap that left many older adults choosing between medications and other necessities.

The program was voluntary from the start. You did not have to join Part D when it began, but Medicare added a penalty for people who waited to enroll: if you go without Part D coverage for 63 days or more and then sign up later, you pay a higher monthly premium for as long as you have the benefit. That penalty structure remains in place today.

Part D is run by private insurance companies under contract with Medicare, not by Medicare itself. This means the plans available to you, the drugs they cover, and the costs vary depending on which plan you choose and where you live.

Key Takeaways

  • Part D started January 1, 2006, filling a gap in Medicare coverage for prescription drugs that had existed since Medicare began in 1965.
  • Enrollment in Part D is voluntary, but delaying enrollment beyond 63 days after you become may be able to access triggers a permanent monthly penalty.
  • Private insurance companies operate Part D plans under Medicare's rules, so coverage and costs differ by plan and location.
  • The benefit structure includes a deductible, a coverage gap (donut hole), and catastrophic coverage, with costs shifting at each stage.
  • You can change Part D plans once per year during the annual enrollment period, which runs from October 15 to December 7.

Why Medicare added drug coverage in 2006

When Medicare started in 1965, prescription drugs were far less central to treatment than they are today. By the early 2000s, medications had become the primary way doctors managed chronic diseases like diabetes, heart disease, and arthritis. Seniors were paying hundreds of dollars per month out of pocket for drugs, and many were skipping doses or not filling prescriptions at all to save money.

Congress passed the Medicare Modernization Act to address this gap. The law was controversial — some people saw it as necessary protection, while others worried about the cost to the federal government and the complexity of having private companies run the benefit. That debate continues, but Part D has been part of Medicare for nearly two decades now.

The 2006 launch was not smooth. Enrollment was confusing, many seniors missed important date, and some plans had problems processing claims in the first months. The experience shaped how Medicare now handles enrollment periods and penalties.

How Part D coverage works in stages

Part D is structured in four cost stages, and your out-of-pocket costs change as you move through them during the calendar year. Understanding these stages helps you predict what you will pay.

Stage 1: Deductible. You pay the full cost of your drugs until you reach your plan's deductible, which varies by plan but is capped at a maximum amount set by Medicare each year. Not all plans have a deductible, and some drugs may be covered before you meet it.

Stage 2: Initial coverage. Once you meet the deductible, you and your plan share the cost. You typically pay a copay (a fixed dollar amount) or coinsurance (a percentage of the drug's cost), depending on the plan and the drug's tier.

Stage 3: Coverage gap (donut hole). When your total drug costs reach a certain amount, you enter the coverage gap. Here, you pay a higher percentage of the cost until your out-of-pocket spending reaches a second threshold. This stage has been shrinking since 2010 — the law that created it included provisions to gradually reduce what you pay in the gap.

Stage 4: Catastrophic coverage. Once your out-of-pocket costs reach the catastrophic threshold, Medicare and your plan cover most of the cost for the rest of the year. You pay a small coinsurance or copay.

Enrollment important date and penalties for late enrollment

When Part D started in 2006, anyone already on Medicare could enroll during an initial enrollment period. Today, if you are turning 65 or becoming may be able to access for Medicare for another reason, you have a seven-month window to join Part D without penalty — this is your initial enrollment period.

If you miss that window and do not have other creditable drug coverage (coverage as good as Part D), you will owe a late enrollment penalty. The penalty is calculated as 1% of the national average Part D premium for each month you were not enrolled. That percentage is applied to your monthly premium permanently, even if you switch plans later. For example, if you delay enrollment by two years, your penalty would be roughly 24% of the average premium, added to whatever plan you eventually choose.

The annual enrollment period for Part D runs from October 15 to December 7 each year. During this time, you can switch to a different Part D plan or drop coverage entirely. Changes take effect January 1 of the following year.

Changes to Part D since 2006

Part D has been modified several times since its launch. In 2010, the Affordable Care Act made changes to reduce costs in the coverage gap — this is why the "donut hole" is smaller now than it was in 2006. In 2022, the Inflation Reduction Act capped out-of-pocket costs at $2,000 per year for Part D, a major change that took effect in 2024.

Drug formularies — the lists of medications each plan covers — change every year. A drug your plan covered last year might not be covered this year, or it might move to a higher cost tier. This is why reviewing your plan annually during the enrollment period matters, even if you have been happy with it.

The number of Part D plans available has also grown. In 2006, there were roughly 40 plans nationwide. Today, most areas have 20 to 30 plans to choose from, though the exact number varies by state and region.

How to find your current Part D plan and coverage information

If you are already enrolled in Part D, your plan information is on your Medicare card and in your plan's member handbook. You can also log into your account at Medicare.gov to see which plan you are in, what drugs are covered, and what your costs are.

Your plan's website or customer service line can tell you whether a specific drug is covered, what tier it is on, and what you will pay. Many plans also have online tools where you can search by drug name and see your copay or coinsurance before you fill a prescription.

If you need to change plans or are considering Part D for the first time, Medicare.gov has a plan comparison tool. You enter your drugs and pharmacy, and it shows you plans ranked by estimated cost. This tool is available year-round, but changes only take effect if you enroll during the annual enrollment period or a special enrollment period.

What to ask your doctor about Part D coverage

When your doctor prescribes a medication, it is worth asking whether it is on your Part D plan's formulary and what your cost will be. If the drug is not covered or is very expensive, ask whether there are alternatives that are covered at a lower cost tier. Sometimes a different drug in the same class works just as well and costs less.

If your doctor prescribes a drug that is not covered, you can ask your plan for an exception. This is called a formulary exception or prior authorization. Your doctor submits a request explaining why this specific drug is medically necessary, and the plan decides whether to cover it. This process can take a few days, so do not wait until you are out of medication to start it.

You can also ask your pharmacist what your copay will be before you fill a prescription. Pharmacists see your plan information and can tell you the cost on the spot. If it is higher than you expected, that is the time to call your doctor and discuss alternatives.

Frequently Asked Questions

What happens if I did not enroll in Part D when I first became may be able to access?

You can still enroll during the annual enrollment period (October 15 to December 7), but you will owe a late enrollment penalty. The penalty is 1% of the national average Part D premium for each month you were not enrolled, and it is added to your monthly premium permanently. The sooner you enroll, the smaller the penalty will be.

Can I switch Part D plans if my drug is no longer covered?

Yes. If your plan stops covering a drug you need, you may be able to request a special enrollment period, which allows you to switch plans outside the normal October-December window. Contact your plan or Medicare to ask whether you may have access to. You can also wait for the annual enrollment period and switch then.

Does Part D cover all prescription drugs?

No. Each Part D plan has a formulary — a list of covered drugs. Plans must cover drugs in certain categories, but they can exclude others or require prior authorization. If a drug you need is not covered, you can ask your plan for an exception, or you can switch to a different plan that does cover it.

What is the difference between Part D and a Medigap drug benefit?

Part D is Medicare's prescription drug benefit run by private insurers. Medigap (supplemental insurance) covers some of the costs Medicare does not pay for hospital and doctor visits, but it does not cover prescription drugs. You need Part D separately if you want drug coverage.

Do I have to use the pharmacy my plan recommends?

Most Part D plans have a network of preferred pharmacies where your copay is lowest. You can use an out-of-network pharmacy, but you will usually pay more. Check your plan's pharmacy directory or call customer service to find in-network pharmacies near you.