"The labels on all OTC drugs have a standard format, and it is fairly easy to tell if two drugs are the same," he says.

In 2002, the FDA introduced a standardized label, which you can find an example of on the FDA site. When you compare medications across brands, focus on the drug's active ingredients as well as the amount in each dosage unit, which will tell you if two medications are identical.

For example, two medications that contain 500 milligrams of acetaminophen, a pain reliever, are identical and should produce the same result in terms of relieving pain.

If you're confused by the labels, bring your questions to the store pharmacist, who "will be happy to step out from behind the counter and show you which medicines are comparable and will be the most helpful given your needs," says Karbowicz.

Pharmacists can also help you pinpoint which medications will be the best for you given your particular symptoms, Jenkins says, and can also counsel you about potential interactions between your OTC and prescription drugs.

A drug's packaging doesn't make a difference in terms of its effectiveness, but is a matter of preference for the individual consumer, who may prefer gel-caps over tablets or redi-tabs over caplets.

"Gel-caps may be easier for you to swallow, but the form really doesn't make a difference in terms of how fast a pill will work or in terms of how it works," says Karbowicz.

Where to shop
Unlike prescription drugs, where online outlets have exerted downward pricing pressures on all retailers, shopping for OTC drugs is best done in person in a local pharmacy, grocery store or big-box store such as Wal-Mart, Kmart, Target or even a warehouse stores such as Costco or Sam's Club, says Findlay.

You can shop for OTC drugs online, but any cost savings are likely to be small even when buying off-brand medications, given the difficulty in comparing medications online and extra shipping costs.

For some products, there are several different off-brand versions, including a store version -- like Rite Aid or CVS brands -- and a more "generic" off-brand version, Findlay notes. The store brand may receive product placement next to the brand name, while the more obscure "generic" off-brand may be on a lower shelf.