You stand at the counter, staring at a $120 price tag for a medication you need every month. Your insurance just shrugged. The pharmacist suggests a discount card. But which one? GoodRx, SingleCare, Optum Perks, Blink Health—each promises huge savings. Yet here’s the part nobody tells you: these cards are not interchangeable, and the one that worked great for your cousin’s antibiotic might be worthless for your blood pressure med. The real game is comparing them in real time, because the same drug can cost $8 with one card and $45 with another at the same pharmacy on the same Tuesday afternoon.

To understand why, you have to know how these tools actually function. They’re not insurance. They’re negotiated pricing agreements between a pharmacy benefits manager and individual pharmacies. When you hand over a card, the pharmacy’s software looks up a contracted price for that drug under that specific plan. Different cards have different contracts, which is why prices swing so wildly. GoodRx has the deepest network of pharmacies, but that doesn’t mean it always has the lowest price. SingleCare often beats GoodRx on brand-name medications, especially for the first fill. Optum Perks, backed by the health services giant, sometimes offers surprisingly low prices on generics but has a smaller network that excludes independent pharmacies. Blink Health works differently—you pay Blink upfront, then pick up the drug at a partner pharmacy with no additional charge. For rare drugs or unusual doses, Blink’s fixed pricing can be a lifesaver. But it also requires a bit of planning, because you can’t just show up and hope.

The dirty secret of these cards is the hidden fees. Several popular cards, including some that advertise “no membership fees,” charge what’s called a “dispensing fee” or “processing fee” at checkout. That $9 price you saw online suddenly becomes $14 when you pick up the prescription. The fee varies by pharmacy and by card, and it’s buried in the fine print. GoodRx was notorious for this for years, though they’ve moved toward transparent pricing at most chain pharmacies. SingleCare and Optum Perks tend to be more straightforward, but you still need to squint at the estimate and look for the line labeled “fees.” Blink Health builds everything into its upfront price, which sounds cleaner, but if you need to cancel or change a prescription, you’re in for a customer service maze.

Here’s where things get stupidly simple and frustratingly complex at the same time. Offten, the biggest savings come from switching your default card from month to month. Say your maintenance medication, a generic for high cholesterol, costs $30 with your current card at CVS. But you’re about to run out. Before you hit the pharmacy, run the same drug through GoodRx, SingleCare, Optum Perks, and Blink with your zip code. You might find that a different card costs $12 at the same CVS. Or you might discover that if you walk ten minutes to a Walmart, the same drug costs $6 with yet another card. That’s not a myth. Pharmacy benefit managers negotiate separate rates with every pharmacy chain, often in the same city. A card that is cheap at a big-box store can be expensive at a regional chain, and vice versa.

Now, about your insurance. A lot of people assume insurance copays are always lower than discount card prices. That’s a dangerous assumption. With high-deductible plans, you might pay the full negotiated price—which can be three times higher than what a discount card would give you. Even with a standard copay, some generics have copays of $25 or $40, while the same drug with SingleCare runs $8. The trick is to ask the pharmacist to check both. They can run your insurance and then run a discount card without billing your insurance. But here’s the catch: you can’t use a discount card with your insurance on the same claim. It’s one or the other. What you can do is use a manufacturer copay card on top of a discount card in some cases, though pharmacies differ on that.

One more thing that separates the pros from the frustrated bargain hunters: every card has a list of excluded drugs. Controlled substances like opioids and stimulants are often excluded or heavily overpriced with discount cards, because the manufacturers don’t want the transparent pricing. Also, some cards won’t touch certain specialty medications. Before you pick your card for the month, do a quick check to make sure your drug is even covered. Finally, don’t ignore cash pricing. Sometimes the pharmacy’s own cash price is lower than any card out there. A few independent pharmacies offer “good faith” pricing that beats the negotiators, especially on antibiotics and short-term meds.

The simple habit that saves ordinary people hundreds each year is this: never fill a prescription without a thirty-second smartphone check. Pop in the drug name, dose, quantity, and your zip code. Compare three cards you already know. Then ask the pharmacist to verify the final out-of-pocket price with the dispensing fee factored in. That single step will eventually pay for itself in one or two fills. Discount cards are not a permanent solution to rising drug prices, but they’re a powerful lever in a sea of confusing pricing—and the only way to win is to pull that lever every single time.