The Durham company, which helps drug makers test and sell new medicines, has attracted more than 125,000 registered users to iGuard.org, a Web site Quintiles started six months ago. IGuard users receive alerts on drug safety and recalls, side effect risk assessments for the medicines they take and information about possible drug interactions; they also can share treatment experiences with each other online.

In return, Quintiles gains access to patients' confidential medical information and their physicians' prescribing habits -- data the pharmaceutical industry is spending millions of dollars every year trying to get, said David Windley, an analyst for Jefferies & Co. in Boston who tracks drug research companies, also known as contract research organizations or CROs. With more than $2 billion in annual revenue, Quintiles is the world's largest CRO.

Dr. Hugo Stephenson, president and founder of iGuard, said the Web site helps monitor the safety of drugs on the market, information that can be difficult to come by.

"It's really, really hard to find out how drugs work in the real world," Stephenson said.

CROs like Quintiles usually gather patient information from physicians. Skipping the physicians and going directly to patients could raise concerns about medical confidentiality.

But Aimee Wall, an assistant professor at UNC-Chapel Hill and a lawyer specializing in medical confidentiality, didn't detect any problems. She said the key is that iGuard users volunteer their confidential medical information.

Stephenson came up with the idea for iGuard when he was president of Quintiles' strategic research services, a business unit that monitors the side effects of medicines already on the market. Once iGuard was established and the Web site launched, he switched jobs to head the new Quintiles subsidiary.

Quintiles had hoped to reach 100,000 iGuard users by the summer, Stephenson said. But given the site's popularity so far, the company now expects the number of registered iGuard users to climb into the millions. Stephenson acknowledged that many users would provide drug safety data that pharmaceutical companies would be very interested in.

Windley said that if the Web site attracts a million or more users, Quintiles could combine data from iGuard and the company's other information sources to help drug makers improve marketing efforts and boost sales.

"It's an ingenious idea," he added.

Much of the information iGuard provides patients can be gotten elsewhere: The Food and Drug Administration and search engines such as Google can e-mail drug safety alerts and recalls to consumers. Pharmacists filling prescriptions are knowledgeable about drug interactions. Physicians can provide risk assessments.

But Susan Reeder of Dover, Del., switched from Google alerts to iGuard five months ago because the information she receives from iGuard is tailored to her particular case and gives her more sense of control.

"It's a needed service," Reeder said.

Guarding privacy

IGuard, which recruits patients at doctors' offices, pharmacies and large employers, tells users that the information they provide may be used for drug research purposes. According to Quintiles, firewall and encryption technology and external auditors are in place to ensure personal and medical information of users cannot be matched by drug makers. Reeder said she read the terms of using iGuard and considers them a price she was willing to pay for the information iGuard offers her.

After the 54-year-old teacher detected a lump in her breast in June 2005, she became even more vigilant about her health. The lump, which turned out to be breast cancer, wasn't picked up on a subsequent mammogram. It took an ultrasound test to confirm what Reeder had found while showering.

Now, she sees six different doctors, three of them to monitor whether the cancer is coming back. So far, a drug she is taking has kept the cancer in check. But the drug, Arimidex, has a list of side effects, including bone loss and elevated cholesterol.

"[IGuard] helps me to stay on top of what's going on," Reeder said. "One doctor may not know what the other was doing."

Reeder said iGuard has already helped her and thinks it will do the same for others.

Two months after she signed up, she received a safety alert on Fosamax, a bone density booster she had been taking since September.

Within a few weeks of starting the medication, she started having serious chest and throat pain and went to the hospital emergency room on one occasion thinking she was having a heart attack. The pain defied every test. When the iGuard safety alert mentioned her symptoms as one of Fosamax's possible side effects, her doctor switched her to another drug.

Reeder said the pain has since disappeared.