Copay vs coinsurance — the difference that costs you
A copay is a flat dollar amount ($25, $50) no matter the drug’s price. Coinsurance is a percentage of the price. Cheap generics sit on low tiers with flat copays; expensive specialty drugs like GLP-1s usually sit on Tier 4 or Tier 5, where your share is coinsurance. On a $1,349 drug, 25% coinsurance is about $337 a month — and the plan still says it "covers" the drug, because it’s paying the other 75%.
Why January is the worst month
Most plans reset your deductible on January 1. Until you’ve paid enough out of pocket to meet that deductible, you generally pay the full allowed amount for the drug — which on a GLP-1 can be the whole four-figure price. Once the deductible is met, your coinsurance percentage kicks in. Once your total out-of-pocket spending hits your plan’s out-of-pocket maximum, the plan pays 100% of covered in-network care for the rest of the year. So the same drug can cost you a lot in January, less by spring, and nothing by fall.
Reading your EOB (it’s not a bill)
The Explanation of Benefits (EOB) your insurer sends is not a bill — it’s a summary of how the claim was processed. It shows the amount billed, the "allowed amount" (the negotiated price), how much the plan paid, and your "patient responsibility." If the number scares you, check whether it’s an EOB (informational) or an actual pharmacy bill before paying, and confirm the drug’s tier with your plan.