People shopping for a Medicare Advantage plan usually start with the doctor network, then the premium, then the extra benefits. The drug formulary tends to come last, if it comes up at all, and that's backwards for a lot of households. If you take even two or three regular prescriptions, the formulary, the plan's specific list of covered drugs and how much each one costs, can swing your total yearly cost by hundreds or thousands of dollars more than the premium ever will.
Here's how to actually check a plan's formulary before AEP, instead of finding out at the pharmacy counter in January.
What a Drug Formulary Actually Is
Every Medicare Advantage plan that includes drug coverage, and every stand-alone Part D plan, builds its own formulary: a list of covered medications sorted into tiers, usually from generic drugs at the lowest cost up to specialty drugs at the highest. The same medication can sit on a low tier with one plan and a much higher tier, or be left off the list entirely, with another plan in the same California county. Two plans can look nearly identical on premium and doctor network and still leave you paying very different amounts for the same prescriptions.
Why This Matters More Than the Premium for Many People
A $0 premium plan is only a good deal if it also covers your medications affordably. We regularly see people save more by moving to a plan with a modest premium and a better formulary tier for their specific drugs than they'd ever save by chasing the lowest premium alone. If you take a brand-name medication, a specialty drug, or a combination of several prescriptions, the formulary comparison usually matters more than any other single factor on your list.
Same drug, different tier
A common example: a cholesterol medication sits on Plan A's generic tier for a small copay, but on Plan B it's classified differently and costs several times more per month, for the exact same prescription.
Covered vs. not covered at all
Some formularies exclude certain brand-name drugs entirely when a generic or therapeutic equivalent exists. If your doctor has a specific reason you need the brand version, this is worth flagging before you enroll, not after.
How to Actually Check the Formulary Before You Enroll
The most reliable tool is the Medicare Plan Finder at Medicare.gov. Enter every medication you take, along with the exact dosage and your regular pharmacy, and it will estimate your real annual drug cost under each available plan, not just the premium. This step alone is often the single most useful thing you can do before AEP.
Before you compare plans, gather:
- A complete list of your current prescriptions, including dosage and frequency
- Your preferred pharmacy, since costs can vary between in-network pharmacies
- Any medications your doctor has mentioned adding this year
- Your current plan's Annual Notice of Change letter, if you have one, to see what's changing for next year
Watch for Prior Authorization and Step Therapy Rules
Beyond the cost tier, check whether a medication requires prior authorization, meaning your doctor needs the plan's approval before it's covered, or step therapy, meaning you may need to try a cheaper drug first and show it isn't working before the plan covers a more expensive one. Both are common and legal, but they can delay getting your medication if you're not expecting them. The Plan Finder tool flags these restrictions alongside the cost tier for each drug.
Formularies Can Change Every Year, Even If You Don't Switch Plans
Plans generally can't remove a drug you're currently taking or move it to a higher cost tier in the middle of the plan year, with limited exceptions like a drug being pulled from the market for safety reasons. But formularies routinely change every January 1, which is exactly why the Annual Notice of Change letter you get each September or October is worth reading closely, even if you're happy with your current plan and have no plans to switch.
Worth checking together: our Part D coverage in California guide covers how drug tiers, deductibles, and the coverage gap work in more detail.
If your household is comparing several plans side by side, our Medicare Advantage plans in California guide is a good starting point for the rest of the comparison, from networks to extra benefits.
If you're helping a Spanish-speaking parent or family member run this same comparison, our sister site Beneficios Medicare covers formulary comparisons in Spanish.
Not sure how your medications stack up across plans?
A licensed Medicare specialist can run your exact prescription list against every plan available in your county, at no cost to you.
Schedule a Free Plan ReviewFrequently Asked Questions
What is a drug formulary?
It's the list of prescription medications a plan covers, organized into cost tiers. The same drug can be priced very differently, or excluded entirely, from one plan to the next.
How do I check if my medications are on a plan's formulary before I enroll?
Use the Medicare Plan Finder at Medicare.gov, enter your exact medications, dosages, and pharmacy, and it will estimate your annual cost under each plan. You can also ask a licensed agent to run the comparison for you.
What does it mean if a drug requires prior authorization or step therapy?
Prior authorization means your doctor needs the plan's approval before it's covered. Step therapy means you may need to try a cheaper drug first. Both can delay your medication if you're not expecting them.
Can a Medicare Advantage plan change its drug formulary during the year?
Plans generally can't remove a drug you're currently taking or raise its tier mid-year, with limited exceptions. Formularies commonly change every January 1, which is why the Annual Notice of Change letter matters.
Do all Medicare Advantage plans in California cover the same drugs?
No. Coverage and pricing tiers vary significantly between plans and carriers, even within the same county, so two similar-looking plans can leave you with very different drug costs.
One More Thought
The formulary is one of the least glamorous parts of comparing Medicare Advantage plans, and one of the most consequential for anyone taking regular medications. Before you renew or switch this AEP, run your actual prescription list against your options rather than assuming your current plan, or the one with the lowest premium, still covers your drugs the same way it did last year.