Prescription drugs, especially for people with chronic conditions like diabetes or blood pressure, can help manage or improve a patient's condition. Studies have shown that a majority of Medicare beneficiaries take at least 1 medicine for a chronic condition, and 25% take 5 or more. However, while clinical trials evaluate the safety of these medications, trials are conducted for only finite time period. Patients who take these drugs for chronic conditions do so for extended periods of time,even lifelong. Additionally, trials are conducted in a controlled environment; real-world patients would provide the actual data on long-term effects, drug-drug interactions, drug-food interactiosn, etc. An apt example of this would be the pain medication Vioxx. Approved in 1999, studies and analyses done after Vioxx hit the market confirmed that it raised the risk of heart attack and nearly 40,000 people died as a direct or indirect result of taking the drug before it was taken off the market in 2004.
In May 2008, HHS and the FDA launched the Sentinel Initiative to improve post-marketing surveillance of prescription drugs and to avoid tragedies like Vioxx. The Sentinel network consists primarily of 18 organizations, including large health insurers (Aetna, Anthem, Humana, and Kaiser Permanente), various disease registries, hospitals, and in-patient facilities.
Read more about the program on Health Affairs