When you’re on Medicare Part D generics, prescription drug coverage under Medicare that includes lower-cost generic versions of brand-name medications. Also known as Part D formulary drugs, it’s the main way millions of seniors and eligible individuals cut their monthly pill costs. Most plans cover generics first because they’re just as safe and effective as brand names—but often cost 80% less. You don’t need to be a pharmacist to understand this: if your doctor prescribes a drug like lisinopril or metformin, chances are your plan will push you toward the generic version because it’s cheaper and just as good.
Not all generics are treated the same under Medicare Part D. Plans group drugs into tiers, and generics usually land in Tier 1 or 2, meaning you pay the least out of pocket. But here’s the catch: if your plan doesn’t list a specific generic on its formulary, you might pay more—or even get denied unless you get prior authorization. That’s why it’s smart to check your plan’s drug list every year during open enrollment. A drug your plan covered last year might be moved to a higher tier, or replaced with a different generic version you haven’t tried yet.
Some drugs, like narrow therapeutic index drugs, medications where small changes in dose can cause serious side effects, like warfarin or levothyroxine, have stricter rules. Even though they’re generics, Medicare plans may require you to stick with one brand of generic because switching between manufacturers can affect how your body responds. This isn’t about cost—it’s about safety. If you’re on one of these, talk to your pharmacist before switching, even if the label says "generic".
Another thing people overlook: formulary changes, annual updates to which drugs a Medicare plan covers and at what cost happen every January. A generic you’ve been using for years might suddenly require a step therapy rule—you have to try another cheaper generic first. Or your plan might drop coverage entirely and force you to pay full price unless you appeal. That’s why keeping a list of your meds and checking your plan’s updated formulary every fall is not optional—it’s your best defense against surprise bills.
And don’t assume all pharmacies are equal. Some Medicare Part D plans have preferred pharmacies that give you the lowest copay for generics. If you’re buying Medicare Part D generics at a non-preferred pharmacy, you could be paying $20 extra per month. That adds up to $240 a year—money you could use for groceries, gas, or a doctor visit. Use your plan’s website or call customer service to find the cheapest place to fill your scripts.
There’s also a gap in coverage—yes, the donut hole still exists. But thanks to recent changes, once you hit it, you pay no more than 25% for generics. That’s a huge improvement from a few years ago. Still, you need to track your spending. If you take multiple generics, you might hit the catastrophic coverage phase faster than you expect, which means your out-of-pocket costs drop even more.
Below, you’ll find real-world guides on how to compare generic versions of common drugs like ibuprofen, levothyroxine, and warfarin—what works, what doesn’t, and how to avoid getting stuck with a version that doesn’t agree with your body. These aren’t theoretical tips. They’re from people who’ve been there: the ones who saved hundreds by switching generics, the ones who got hit with a $150 bill because they didn’t check their formulary, and the ones who learned the hard way that not all "generic" means the same thing.
Discover how insurance plans decide whether to cover generic combination drugs or individual generics-and why you might pay more for a combo pill even when it contains the same ingredients. Learn how to save on prescriptions in 2025.
