Wal-Mart Stores Inc., the world's largest retailer, announced Monday it would expand its discounted prescription drug program to offer 90-day supplies for $10 and add several women's medications at a discount. It also said it would lower the price of more than 1,000 over-the-counter drugs.

Target Corp. said late Monday it would match the major elements of Wal-Mart's program.

Wal-Mart's move marks the third phase of a company program that began in 2006 to provide a 30-day supply of generic prescription drugs for $4. The Bentonville-based company said the program has saved customers more than $1 billion.

With the expansion, the company began filling prescriptions Monday for up to 350 generic medications at $10 for a 90-day supply at Wal-Mart, Neighborhood Market and Sam's Club pharmacies in the U.S. Almost all the prescription generics in the company's $4 program were included in the expanded $10 offer, said Wal-Mart Senior Vice President John Agwunobi.

In addition, the company will add several women's medications to its list of prescriptions available for $9, including drugs to treat breast cancer and hormone deficiency.

For instance, alendronate, the generic version of osteoporosis medication Fosamax, will be added to the list. Company pharmacies will fill 30-day prescriptions of alendronate for $9 and a 90-day supply for $24 at a comparison of $54 and $102, respectively, that women previously paid for the same amounts, the company said.

Tamoxifen, used to treat breast cancer, will be offered for $9 for a 30-day supply, as well as combination estrogen/methyltestosterone tablets, prescribed for menopause and hormone deficiency.

Wal-Mart also will lower the prices of more than 1,000 over-the-counter medications to $4 or less in its pharmacies, company officials said. The company has sold over-the-counter medicines in the past at discounted prices, but revised and expanded its offerings specifically to include commonly used drugs that usually sell for $7 or more, said company spokesman Deisha Galberth.

The over-the-counter medication price rollbacks represent about one-third of the retailer's over-the-counter medicines. They include Wal-Mart's Equate versions of popular drugs, including Zantac, Pepcid and Claritin, and Wal-Mart's Spring Valley prenatal vitamins.

Since 2006, Wal-Mart's $4 generic drug program has expanded to every state, except North Dakota, where Wal-Mart has no in-store pharmacies. And many company competitors have followed the retailer's lead.

Target said it will expand its assortment of $4 prescriptions, offer 90-day supplies for $10, and sell over-the-counter medications for $4 or less. The company said more details about which drugs will be included will be released soon.

While stressing that the expansion was designed to help customers at a time of exorbitant health-care costs and difficult economic times, Wal-Mart's Agwunobi said the program has worked in everyone's favor.

"This is the time for us now to begin building capacity," he said. "It offers (customers') employers potential savings. It offers the customers significant savings. It also offers us the ability to add capacity to our pharmacies without adding people."

Agwunobi expects the 90-day discount will increase the company's market share of mail-order and online prescriptions as customers realize the value of the company offer.

Wal-Mart Chief Operating Officer Bill Simon said the results in each phase of the program have been strong and prescription volume has increased, "exceeding our expectations." He said the company would not, however, offer free generic drugs at its in-store clinics as some competitors have.

"We're in business to make money," Simon said. "Free is a price that is not a long-term sustainable proposition."

Shares of Wal-Mart fell 53 cents to $56.97 Monday.