Generic vs. Brand Drugs in Part D: How Tiers Set Price

"My neighbor pays $5 for the same prescription that costs me $45." Price gaps like that are one of the most common Part D frustrations — and almost always, the answer comes down to drug tiers. Here's how they work.

What "generic" and "brand" actually mean

A brand-name drug is the original product developed by a pharmaceutical company, protected by a patent for a number of years. When that patent protection ends, other manufacturers can make a generic version. The FDA requires every generic to have the same active ingredient, strength, dosage form, and route of administration as the brand, and to be bioequivalent — meaning it reaches the part of the body where it works in the same amount of time and in the same amount as the brand-name drug. Inactive ingredients, color, and shape can differ, but the medicine itself meets the same quality standards — and about 9 in 10 prescriptions filled in the U.S. are for generics.

One nuance: "brand vs. generic" is not the same as "expensive vs. cheap." Some generics are costly, and some brands land on a preferred tier at a reasonable copay because the plan negotiated a good price. What matters for your wallet is the tier, not the label.

The five tiers, explained

Nearly every Part D plan uses a five-tier formulary. Each plan decides which drugs go in which tiers, so details vary, but the structure is consistent:

• Tier 1 — Preferred Generic: commonly used, low-cost generics. Lowest copays — often $0 to $15 for a 30-day supply.
• Tier 2 — Generic: other generics, slightly higher cost. Still a modest fixed copay.
• Tier 3 — Preferred Brand: brand-name drugs without a generic equivalent that the plan negotiated favorable pricing on. Moderate copay — and covered insulin products are capped at $35 per month in 2026.
• Tier 4 — Non-Preferred Drug: non-preferred generics and brands. Usually coinsurance (a percentage of the drug's cost, such as 25–40%).
• Tier 5 — Specialty Tier: unique or very high-cost drugs. Also coinsurance, often the plan's highest percentage.

Copays (flat dollar amounts) apply mainly to Tiers 1–3; coinsurance (a percentage) is common on Tiers 4–5. With coinsurance, your cost rises and falls with the drug's price.

Why a drug lands in a particular tier

Plans negotiate prices with drug manufacturers, and those negotiations shape the formulary:

• Two plans can place the same drug in different tiers — which is why comparing plans during open enrollment (October 15 – December 7) matters.
• A brand-name drug with no generic equivalent can still land on Tier 3 (preferred) rather than Tier 4 if the plan got a good deal.
• A higher-priced generic can land in Tier 2 or even Tier 4 instead of Tier 1.
• Plans can also move a drug to a different tier during the year. If they do, they must notify affected members, prescribers, and pharmacists 60 days in advance of the change — and they generally cannot make formulary changes during the first 60 days of the contract year.

Your position in the benefit also matters. In 2026, the standard deductible maxes out at $615, and once you and others on your behalf have paid a combined $2,100 out of pocket for covered drugs, you enter catastrophic coverage and pay $0 for Part D drugs for the rest of the year. Tier coinsurance counts toward that cap.

When the brand name is the right choice

Generics are appropriate for most people, but there are situations where the brand (or a non-preferred drug) makes sense:

1. No generic exists. Many newer drugs are still under patent and only available as brands — the plan's tier determines what you pay.
2. Your doctor requires it. If you've had side effects from a generic's inactive ingredients, your plan can cover the brand — though it may sit in a higher tier, and a formulary exception may be needed.
3. Narrow therapeutic index drugs. For a small number of medicines (certain seizure or thyroid drugs, for example), even tiny dose variations matter, and doctors sometimes prefer you stay on one specific version. This is a conversation for your prescriber and pharmacist.

Also note: if the actual cost of a drug is less than your tier's normal copay, you pay the actual (lower) cost, not the higher copay. Pharmacies apply this automatically.

What to do if your drug changes tiers

Tier changes usually arrive by letter — the required 60-day notice. When one does:

• Read the letter carefully. It should name the drug, the new tier, the effective date, and your alternatives.
• Ask your pharmacist whether a lower-tier generic or preferred brand treats the same condition.
• Talk to your doctor before switching — they can confirm whether the alternative is appropriate or whether you should request a formulary exception to stay on your current drug.
• Compare plans during open enrollment. A drug that sits on Tier 4 in your current plan might be Tier 2 in another. Enter your full drug list on Medicare.gov's Plan Finder to see real numbers.
• Check Extra Help. If your income and resources are limited, Extra Help can lower or eliminate Part D premiums, deductibles, and tier copays.

Bottom line: In Part D, the tier decides the price — generics usually sit cheapest, but plan negotiations can surprise you, so check each drug's tier every year and act on those 60-day notices.