You might be paying more for your prescriptions at the pharmacy if you use your health insurance than if you pay cash out of pocket.

How can that be?

Say your doctor prescribes a generic drug and, using your health plan, your copay for generics is $10 per 30-day supply. If you submit your purchase through your insurance, you will pay the $10. But many discount stores, pharmacy chains and supermarkets have deals for common generics that could cost less. Stores including Wal-Mart, Costco, K-mart and Target have programs that offer about 150 to 300 generic drugs at the discounted price of $4 per 30-day supply.

The retailers do this as a marketing ploy, explains Charles Coonrod, principal of Foundation Strategies in Katy, Texas. "They get you to come in for the drugs and expect you'll buy other things while you're there."

hus, your generic-drug copays through your health plan can be higher than the price of the drug. Health plans often set an average price to cover the cost of most drugs in the tier, which means that some drugs could be sold for less.

Ultimately it depends on the drugs, your health insurance plan, and where you buy it, says Dr. David Belk, who has an internal medicine practice in the San Francisco Bay Area and maintains the website True Cost of Healthcare.

Generic drugs for common conditions
The generic drugs in many retailers' discount programs are prescribed for the most common chronic conditions including arthritis, heart disease, hypertension, diabetes and depression, Belk says. (The drug-discount programs aren't necessarily nationwide because some states have laws prohibiting retailers from pricing drugs below cost.)

If you're taking four pills a day, as many people do as they age, according to the AARP, you can save $6 per prescription. That's $72 a year per medication or $328 for four. You could save more if your copay is higher for generics, and some are.

But if you want to take advantage of a retailer's drug-discount program, you have to tell the pharmacist you don't want to use your health insurance. Your health plan and your pharmacy would prefer that you don't do that, Belk says. "They get more money when you use your health insurance."

But there's nothing to stop you. "Your health insurance can't force you to do anything," Belk says. His advice: Don't tell the pharmacy where you're buying the generics that you have health insurance. "It's not like they're the National Security Administration and they're monitoring you everywhere you go," he says. What they don't know won't hurt them.

Brand-name medicine for less
If the prescription medicine you take is brand-name and doesn't have a generic, you still may be able to get it for less by not using your health insurance. Many plans have copays that are a percentage of the cost of the drug. The cost of some brand-name drugs can be quite high even if you're only paying a percentage.

There are discount-drug cards available that can get you substantial discounts on generic and brand-name drugs at participating pharmacies in their networks, says Kev Coleman, head of research and data at HealthPocket, which helps consumers save money on their health care. For example, the Easy Drug Card offers discounts of up to 75 percent at more than 57,000 participating pharmacies.

The only catch is you can't use both your health insurance and the discount cards. What you need to do, Coleman says, is call different pharmacies and ask about their prices for the drugs you were prescribed. Give them your insurance information and ask for the price with and without it. Your price will be different if you have Aetna than if you have Cigna, for example, and will depend on the rules of your individual plan. Copays can also vary among plans from the same insurer.

After you get the cost with your health insurance, ask if they take a discount card. If they do, ask for the price for the same drug with the discount card. You may need to keep a spreadsheet if you're pricing several drugs and calling several pharmacies.

Do your research
Never assume a pharmacy is going to tell you the cheapest way to buy your medications. You have to play investigator and do it yourself, Coleman says.

Call more than one pharmacy, too, Coleman says. "There can be significant price variations between pharmacies in the same town," he says. You have to be a responsible consumer, he says. "The only cost for talking to multiple pharmacies is your time and that can be a lot cheaper than the cost of some of these drugs."

There also are websites that list the cost of some drugs. A search for the cholesterol-lowering atorvastatin (known by the brand name Lipitor) on GoodRx.com found prices ranging from $76.78 at Rite-Aid to $15.30 at Kmart for a 30-day supply of 20 milligrams. A search for the beta-blocker metoprolol (Lopressor) found a 60-day supply of 25 milligram pills ranged from $3.50 for mail order from HealthWarehouse to $9.99 at Rite-Aid with free membership in its drug program. Your health insurance plan website also might have a drug-cost calculator for comparing prices.

Reaching out-of-pocket limits
Unfortunately, there can actually be a catch to saving money. If you don't use your health insurance to make your purchase, the money you spend won't count toward your out-of-pocket annual limits. Starting this year, under the Affordable Care Act, most plans have annual limits on the amount that people have to pay out-of-pocket for prescription drugs.

Coleman doesn't see a problem because most people don't reach their out-of-pocket limits by the end of their plan year. But if you are taking a lot of expensive medications and have been hospitalized, you could be close to reaching your limits. If you are and it's still early enough in the year, you might want to just pay the higher price for the medications and reach your out-of-pocket limit sooner so that your health insurance kicks in 100 percent. It's really a matter of doing the math, Coleman says.

Safety could also be an issue, says Coonrod. If you use different pharmacies for your different drugs, there's no system in place to check for drug interactions, and "no red flag to potential adverse reactions."

But if you're among the growing number of people coping with a high-deductible health plan, it pays to take the time and figure out how to get the medications you need for the least amount of money, Coleman says.

This article Surprise: Pay Less for Medicine by Not Using Health Insurance originally appeared on Insure.com.

You may also enjoy these health care articles:

Job change and Obamacare: How to deal with a health insurance gap

How to buy individual health insurance

Surviving your high-deductible health plan