MIAMI (AP) — With the promise of affordable health insurance under President Barack Obama’s law, many Americans with serious illnesses are finding relatively low monthly premiums and, in many cases, access to insurance for the first time.

But some have been shocked at how much their prescriptions are costing as insurers are creating complex drug tiers and in some cases charging co-insurance rates as high as 50 percent, leaving patients on the hook for thousands.

Avalere Health, a market research and consulting firm, estimates some consumers will pay 50 percent of the cost of their specialty drugs — that compares to about 30 percent in the private market.