Why Insurers Prefer Certain Generic Drugs: How Formularies Control Costs and Coverage

Most people don’t realize that the generic drug they pick up at the pharmacy wasn’t chosen by their doctor alone. It was selected by a committee of pharmacists and doctors working behind the scenes for their insurance company. These lists-called preferred generic lists-are the backbone of how insurers keep drug costs down while still covering essential medications. If you’ve ever been surprised by a $5 copay for a generic pill that used to cost $150, this is why.

How Insurance Formularies Work

Every health insurance plan, whether it’s Medicare, Medicaid, or a private plan from Blue Cross or UnitedHealthcare, uses a formulary. Think of it as a ranked list of drugs the insurer will pay for, with the cheapest options at the top. The top tier-Tier 1-is almost always filled with preferred generic drugs. These are FDA-approved copies of brand-name medications that work the same way but cost 80-85% less. In some cases, when six or more generic versions of a drug are on the market, the price can drop by as much as 95%.

Insurers don’t just pick generics randomly. They rely on Pharmacy Benefit Managers (PBMs)-companies like CVS Health’s Caremark, OptumRx, and Evernorth-to negotiate prices and build these lists. PBMs use data on safety, effectiveness, and cost to decide which generics make the cut. A drug doesn’t need to be the cheapest to be preferred; it just needs to be proven safe, effective, and cost-efficient.

The Tier System Explained

Most formularies have four or five tiers. Here’s how they break down:

• Tier 1: Preferred generics - $5 to $15 for a 30-day supply. This is where most common medications live: lisinopril for blood pressure, atorvastatin for cholesterol, levothyroxine for thyroid issues.
• Tier 2: Preferred brand-name drugs and some higher-cost generics - $25 to $50. These are drugs that don’t have a generic yet, or where the generic isn’t as widely used.
• Tier 3: Non-preferred brand-name drugs - $50 to $100. If your doctor prescribes a brand-name drug that has a generic alternative, you’ll pay more here.
• Tier 4: Specialty drugs - $100+, sometimes a percentage of the total cost. These include biologics like Humira or Enbrel, used for autoimmune diseases.

The system is designed to nudge patients-and doctors-toward the most affordable options. In 2023, 98% of commercial insurance plans and 100% of Medicare Part D plans used this tiered structure. The goal? Save money without sacrificing health outcomes.

Why Generics? The Numbers Don’t Lie

In 2023, generics made up 90% of all prescriptions filled in the U.S. But they accounted for only 23% of total drug spending. That’s the power of preferred lists. A 2022 study found that patients paid an average of $199 per fill for a generic drug, compared to $393 for the brand-name version. That’s nearly $200 saved per prescription.

Take levothyroxine, a common thyroid medication. One Reddit user reported dropping from $187 a month for the brand to $12 for the generic. That’s over $2,000 a year saved. For chronic conditions-like high blood pressure, diabetes, or depression-those savings add up fast for both patients and insurers.

The FDA requires generics to be bioequivalent to brand-name drugs, meaning they deliver the same amount of active ingredient into the bloodstream within a tight range (80-125%). In 98.5% of cases, studies show they work just as well. So why do some people still hesitate?

The Catch: When Generics Don’t Work as Expected

Not every drug plays nice with generic substitution. For drugs with a narrow therapeutic index-like warfarin (a blood thinner)-even small changes in dosage can cause serious problems. A 2022 report from the American College of Clinical Pharmacy found that 23% of doctors avoid switching patients to generics for these drugs, fearing instability in blood levels.

Another issue: biosimilars. These are the generic versions of complex biologic drugs like Humira. While they’re cheaper, they don’t come with the same co-pay assistance programs. Brand-name biologics often have manufacturer coupons that cut monthly costs from $1,200 to $50. Biosimilars like Amjevita might list for $850, but without those coupons, patients pay the full price. One patient shared on Reddit that switching to the biosimilar actually increased their out-of-pocket costs because their insurer didn’t count the discount toward their deductible.

And then there’s step therapy. Some insurers require you to try the generic first-even if your doctor says it won’t work for you. The American Medical Association found that 42% of doctors have seen treatment delays because of this. For someone with chronic pain or rheumatoid arthritis, waiting weeks for approval can mean more suffering.

What Patients Can Do

You don’t have to accept whatever your plan says. Here’s what actually works:

1. Check your formulary before enrolling. During open enrollment, look up your medications on your plan’s website. If your drug isn’t on Tier 1, consider switching plans.
2. Ask your pharmacist. In 89% of states, pharmacists can swap a brand-name drug for a generic unless the doctor says “dispense as written.” Many patients don’t know this option exists.
3. Appeal denials. If your insurer denies coverage for a non-preferred drug, your doctor can submit a letter of medical necessity. In 68% of cases, these appeals are approved.
4. Use GoodRx or SingleCare. Sometimes the cash price at Walmart or CVS is lower than your copay. Always compare.

Patients who spend just 45 minutes a year reviewing their formulary save an average of 32% on medications. That’s not a small thing.

What’s Changing in 2025 and Beyond

The rules are shifting. Starting in 2025, Medicare Part D plans will be required to place biosimilars in the same tier as their brand-name counterparts. That could push biosimilar use from 15% to 45%-a massive change. But there’s a catch: many PBMs are now using “accumulator adjuster” programs, which don’t count biosimilar costs toward your out-of-pocket maximum. That means you could pay more upfront and still hit your cap later with a brand-name drug.

UnitedHealthcare is testing something new: “value-based formularies.” Instead of just picking the cheapest drug, they’re starting to reward medications that actually lead to better health outcomes-like fewer hospital visits or better blood sugar control. It’s early, but it could change how formularies are built forever.

The Bigger Picture

Insurers aren’t trying to be villains. They’re responding to a system where drug prices have spiraled out of control. The U.S. spends more on pharmaceuticals than any other country-and generics are the only real lever we have to pull. The $1.68 trillion saved annually by using generics isn’t just a number. It’s millions of people who can afford their prescriptions.

But the system isn’t perfect. When a patient with a rare condition gets stuck because their drug isn’t on the list, or when a biosimilar savings gets erased by a hidden policy, the cost isn’t just financial-it’s emotional. The goal should be balance: affordability without compromising care.

For now, the best strategy is simple: know your formulary. Know your options. And don’t be afraid to ask questions. Your wallet-and your health-will thank you.