The Affordable Care Act bans insurance companies from discriminating against patients with pre-existing conditions. But some policy experts say insurers could be doing just that by forcing people with chronic illnesses to pay more for their drugs.

ProPublica's Charles Ornstein explains that insurers have long used a tiered pricing system to steer consumers away from expensive brand name medications. But according to a recent editorial in the American Journal of Managed Care, several prominent health plans are taking this tactic one step further and charging higher co-payments for some generic drugs.

The editorial's authors examined six health plans to see how much they were charging for generic drugs to treat 10 conditions. For certain conditions like epilepsy and HIV, some plans didn't offer any generic drugs in the preferred category -- leaving patients to pay more or find a new plan.

"There are a number of advocates that contend that insurance companies are, while not explicitly charging people more to sign-up or charging them higher premiums, that they're using the way they structure their drug benefits to in fact charge people with pre-existing conditions more," Ornstein says.

The companies say they aren't targeting patients with pre-existing conditions.

So what can you do to make sure you're getting the best price for your prescriptions?

First, Ornstein recommends that you carefully examine your insurer's list of covered drugs, known as a formulary, before enrolling or renewing your health plan. Don't just let your existing coverage roll over because you were satisfied the year before. Plans can change a lot from one year to the next.

Second, consider changing pharmacies or selecting a store like Walmart or Costco that have low-cost or even no-cost generic drugs.

Lastly, talk to your doctor. If your copay has increased, ask your physician for alternative drugs.

Listen to this podcast on iTunes, SoundCloud or Stitcher. And for more on how insurers are shifting costs to consumers, read Ornstein's latest report.