You pick one path per fill
A manufacturer copay card lowers your out-of-pocket when you run the drug through commercial insurance. A cash discount card lowers a cash price when you’re NOT using insurance. You can’t do both on the same fill — the pharmacy system adjudicates one way or the other, so you choose the cheaper path for that fill. And manufacturer copay cards are, by federal law, only for people with commercial insurance: they’re barred on Medicare, Medicaid, TRICARE, and the VA under the Anti-Kickback Statute.
The accumulator / maximizer trap
Here’s the part that catches people. Normally, money paid toward your drug — including a manufacturer copay card’s dollars — would count toward your deductible and out-of-pocket maximum. A copay accumulator program stops that: the card’s dollars pay the pharmacy, but your plan doesn’t credit them toward your deductible. So you feel fine while the card lasts, then it runs out mid-year and you suddenly owe the full amount with little or nothing credited toward your deductible.
A copay maximizer is a cousin: it spreads the card’s maximum annual value evenly across the year (often by labeling the drug "non-essential") and likewise keeps those dollars from counting toward your deductible. Both are real, growing PBM benefit-design practices.
What protection you have (and don’t)
About 21 states have banned copay accumulators, requiring copay-card value to count toward your cost-sharing. But two big gaps remain: the bans mostly target accumulators and don’t reach maximizers, and they generally apply only to state-regulated plans — not self-funded employer plans, which are governed by federal ERISA law. So even in a "ban" state, a self-funded plan or a maximizer can still keep your card dollars from counting. Federal rulemaking on this is still pending. Check your plan documents for "accumulator" or "maximizer" language, and ask your benefits administrator directly.