The drug list is the whole game.
You can pick the wrong Part D plan based on the lowest monthly premium and end up paying more out-of-pocket than you would have on a higher-premium plan that actually covers your medications. We see it every year. The cheapest premium is rarely the cheapest plan.
This article walks you through how Part D works in 2026, how to pick a plan against your actual drug list, what to know about the St. Louis pharmacy network landscape, and how to spot the cost traps before they show up at the counter.
The 60-second framing
Part D is your prescription drug coverage under Medicare. You get it either as a stand-alone plan (paired with Original Medicare and a Supplement) or built into a Medicare Advantage plan. Every Part D plan has a formulary — its list of covered drugs sorted into tiers — plus a deductible, a copay or coinsurance structure, and a pharmacy network.
For 2026, every Part D plan has a $2,100 annual out-of-pocket cap. Once you hit it, the plan covers 100% of your drug costs the rest of the year.
To pick the right plan, you don't compare premiums. You compare your drug list against the formulary.
What is Part D, exactly?
Part D is the drug coverage program. It was added to Medicare in 2006 and is delivered by private insurance companies under contract with CMS. Every plan has to cover the standard set of drug categories (the "protected classes"), but the specific drugs within each category vary by plan.
You enroll in Part D either by:
- Buying a stand-alone Part D plan (a PDP — Prescription Drug Plan) to go alongside Original Medicare, or
- Enrolling in a Medicare Advantage plan that includes drug coverage (an MA-PD).
If you don't enroll in Part D when you're first eligible — and you don't have other creditable drug coverage — you'll pay a permanent late-enrollment penalty when you do enroll. (See our late-enrollment penalties article for the math.)
How drug coverage works in 2026
Three phases. Here's the cost structure for 2026:
Deductible
Some plans waive the deductible on lower-tier drugs (typically Tier 1 and Tier 2 generics). You pay the full negotiated cost of each prescription until you've spent the deductible.
Initial coverage
Once you've met the deductible, you pay copays or coinsurance per the plan's tier structure. The plan pays the rest. This is most of the year for most people.
Catastrophic cap
Once your out-of-pocket spending on covered drugs reaches $2,100 in the calendar year, the plan covers 100% of your covered drug costs the rest of the year.
The out-of-pocket cap is the part that changed for 2025 and continues in 2026. The 2025 cap was $2,000; for 2026 it is indexed to $2,100. It replaced the old donut-hole model. The Medicare Prescription Payment Plan also lets you spread your out-of-pocket costs across monthly installments through the year, instead of paying large amounts in January.
How to pick a drug plan
Three steps, in order:
Write down every prescription you take
Name, dose, frequency. Include over-the-counter drugs only if you have a written prescription. Include drugs you take occasionally if they're expensive.
Run your list through plan formularies
Medicare.gov's Plan Finder is the tool we use in our office. Enter your drugs and preferred pharmacy; it ranks plans by projected total annual cost.
Read the network and restrictions before enrolling
Preferred pharmacies cost less. Standard-network pharmacies cost more. Out-of-network may not be covered at all. Check prior-auth and step-therapy flags on your specific drugs.
Common mistake: people pick the lowest-premium plan without running the formulary check. A $0 or $10 premium plan (Part B will still have a cost) that doesn't cover your insulin, or covers it on Tier 4 with a coinsurance percentage, can cost thousands more across the year than a $45 premium plan with that same drug on Tier 2.
Common St. Louis pharmacy networks
Where you fill your prescriptions changes the math.
The major pharmacy options in St. Louis
- WalgreensNational chain · preferred on some plans, standard on others.
- CVSNational chain · preferred on CVS-affiliated insurer plans.
- SchnucksRegional grocery pharmacies · preferred on a subset of Missouri plans.
- DierbergsRegional in-store pharmacies · similar local presence.
- BJC / Mercy / SSMLimited outpatient retail · check the specific location.
- Independent pharmaciesMany neighborhoods have them · network status varies plan to plan.
- Mail-orderMost plans have a preferred mail-order partner · 90-day fills, useful for stable medications.
If you have a preferred pharmacy already, run the Plan Finder check with that pharmacy selected. The price changes — sometimes a lot — depending on which pharmacy you list.
Tiers, prior authorization, step therapy
Three things on the Summary of Benefits to look for:
Tier structure
Most plans use a 5-tier structure: Tier 1 (preferred generics), Tier 2 (generics), Tier 3 (preferred brands), Tier 4 (non-preferred drugs), Tier 5 (specialty). Your copay or coinsurance depends on the tier. Look up each of your drugs by tier — not by name in the formulary alone.
Prior authorization (PA)
The plan requires the prescriber to get approval before the prescription is filled. Common on Tier 4 and 5 drugs, certain controlled substances, and some specialty medications. If your prescription has PA on a plan, your prescriber will need to send paperwork. Delays of a few days are common — not a problem unless you need the medication immediately.
Step therapy
The plan requires you to try a less-expensive alternative first. If the alternative doesn't work or causes problems, the plan will cover the more expensive option. Common with newer brand-name drugs.
Look for these restrictions on your specific medications before enrolling, not after.
Help paying for drugs — Extra Help / LIS
Extra Help (also called the Low-Income Subsidy or LIS) is a federal program that reduces or eliminates Part D premiums, deductibles, and copays for people who qualify based on income and resources.
For 2026, the full Extra Help benefit is available to people with income up to 150% of the federal poverty level. The income and resource limits change annually — Social Security publishes the current thresholds.
If you qualify for Extra Help, you also automatically qualify for the Medicare Savings Programs (MSP) that help pay Part B premiums in many cases.
We screen every client for Extra Help eligibility in our intake. If there's any chance you qualify, the form is worth filing. Application is free, and we'll help you fill it out.
How we review drug plans together
When you sit down with us, the Part D review looks like this:
- We confirm your drug list — exact names and doses.
- We confirm your preferred pharmacy.
- We run the Plan Finder against the plans available in your county (or for your Advantage plan's included drug coverage).
- We sort by projected total annual cost — not by premium.
- We flag any restrictions (PA, step therapy, quantity limits) on your specific medications.
- We talk through the trade-offs honestly: is the lowest-total-cost plan actually the right plan, given the pharmacy network, the formulary stability, and the carrier's record?
Then you decide. We never enroll on your behalf without your explicit go-ahead.
A note on annual review
Plan formularies change every year. So do your medications. The plan that was the right plan for you in 2026 may not be the right plan for 2027.
We do an annual review for every active client during AEP (October 15 – December 7) and walk through whether their current plan is still the best fit. Even if you don't work with us, do this review yourself with Medicare.gov's Plan Finder every fall. It takes about 30 minutes. It's worth it.
I've been helping people with Medicare in St. Louis since 2013. The drug-plan landscape changes the most year over year of anything in Medicare. Don't set it and forget it.
No fee, no pressure, no sales pitch — that's the rule of the house. We answer every call.
Why not just do it yourself?
You can — we just told you to run the Plan Finder yourself every fall. But know this: using a licensed agent to pick or switch your drug plan costs you nothing extra. We're paid by the plan, not by you; your premium is exactly the same whether you enroll through us or on your own, and it's against the rules for an agent to charge you a fee. So the real choice is: sort through two dozen drug plans alone, or have someone who does it every day run your exact prescription list and pharmacy against all of them — for the same price.
That's where Part D is won or lost: the right plan for your drug list, not the lowest sticker premium. We find it, flag the restrictions, handle the enrollment, and we're here next year when your medications or the formulary change. Don't do it alone — let's do it together.
