Four blockbuster drugs went generic this year, and 10 more will be eligible in the next few years, potentially saving consumers an estimated $49 billion by 2010. But don’t assume you’ll get your share of those savings just by buying generic. You need to shop at the right pharmacies and ask the right questions.

Consumer Reports asked 132 pharmacies about the prices of five common prescription generic drugs and found striking differences. For a family paying out-of-pocket for all five, the difference between the highest and lowest prices could total nearly $2,200 a year. That’s on top of the substantial savings the family would gain by choosing generic rather than brand-name versions of those medications in the first place (see Generic drug savings).

When a drug first goes generic, the maker’s suggested retail price might be 70 percent of the branded version. As competition among generic manufacturers heats up, that price generally falls to 20 to 50 percent of the brand-name equivalent. People with drug insurance or a safety-net program pay only a co-payment or a negotiated price. But if you have no such coverage, you’re on your own.

Some generic drugs cost pharmacies pennies per pill, but they can sell them to people who lack coverage for as much as they want. Some pharmacies will charge far more than others, as we found in our survey of five drugs: fluoxetine for depression, lisinopril for hypertension, lovastatin for high cholesterol, metformin for type 2 diabetes, and warfarin for preventing dangerous blood clots.

Prices for a 30-day supply of those five varied sharply, from $43 at a Costco in Sacramento, Calif., to $296 at an independent pharmacy in Clayton, Mo. Costco stores nationwide were generally the least expensive, with a median price less than half that of the two closest competitors, Wal-Mart and Target. And Costco pharmacy customers don’t have to pay Costco’s $50 annual membership fee.

Overall, online pharmacies, particularly those affiliated with conventional stores, and mass merchants, which sell many different products, tended to charge the least, followed by independents, supermarkets, and drug chains (see Drugstore costs). However, you might find bargains in each category. For example, medications tended to cost substantially less at CVS than at other drug chains, with prices rivaling those of many mass-market and online stores. Conversely, the online store Cigna Tel-Drug was one of the priciest in our study. Independent pharmacies charged anywhere from $82 to $296.

Prices fluctuated dramatically even within the same chains and the same stores. At ShopKo, for example, prices for the five drugs ranged from $80 in Marquette, Mich., to $150 in Redding, Calif. One independent pharmacy in Denver charged more for fluoxetine than the other independents, but less for lovastatin than the vast majority of drugstores that we surveyed.

Price discrepancies aren’t the only obstacle to potential savings from generic drugs. A bottleneck at the U.S. Food and Drug Administration and stalling tactics by brand-name drugmakers are delaying the approval of numerous generic drugs (see our November 2006 Have You Heard?). That affects even people who have prescription-drug coverage, because the typical co-payment is up to $25 less for generic drugs than for brand-name equivalents. Generic medications can also save you money indirectly by helping to reduce overall health costs and, in turn, insurance premiums.

First check our free CR Best Buy Drug reports to find out whether generics are more cost-effective for treating your condition than drugs available as brand name only. Then ask your physician or pharmacist about switching to those or other generic versions of the drugs you need.

The following steps can further help cut the cost of both your generic and brand-name medications:

Compare prices. Call pharmacies or visit their Web site. Some sites list phone numbers so you can ask about prices instead of searching online. To quickly compare prices and order prescription medications at online pharmacies and other drugstores, consider Consumers Union’s free Shop Online service, which should be available soon. Go to the Consumer Reports Medical Guide, find your drug, and click on the Shop Online symbol.

Ask for the cheapest form. We found that prices of the same drug might vary substantially depending on whether it’s a capsule or tablet.

Ask your pharmacist to match lower prices. That makes sense if you want to stick with one pharmacy, which might reduce the chance of taking incompatible drugs. Wherever you buy drugs, note all the medications and supplements you take so that the pharmacist can check for potential interactions.

Buy in bulk. Ask your physician to prescribe 90-day supplies of your medications, which typically cost much less than the 30-day supplies that are often prescribed. If you’re insured, ask whether your insurer will mail medications directly to you and, if so, whether that would save you money or help reduce overall health-care costs.

Check drug-assistance programs. Ask your state or local health-care office about programs that might provide prescription-drug assistance if you’re uninsured. For programs offered by drug companies or pharmacy benefit managers, go to www.pparx.org or www.rxoutreach.com, respectively.

Check federal programs. To see if you’re eligible for drug savings from programs such as Medicaid or Medicare, go to Centers for Medicare & Medicaid Services. If you sign up for a Medicare drug plan or discount drug card, try to re-evaluate the offerings about three times a year, though that can be difficult. To compare prices, go to Medicare.gov. If you can get better coverage or prices elsewhere, switch plans during the open enrollment period. Veterans can ask about programs from the Department of Veterans Affairs or 877-222-8387.