Once a prescription drug hits the market, it’s hard for pharmaceutical companies and government agencies to monitor the thousands of patients who use it to pick up on harmful side effects. But a single allergic reaction can require an expensive hospitalization or even result in a patient’s death.

To better monitor these risks, the Food and Drug Administration is turning to an online social networking and data-sharing site for patients. The agency announced on Monday that it will tap data provided by a website called PatientsLikeMe to detect so-called adverse events for prescription and over-the-counter medicines that the agency and drug manufacturers may have missed during clinical trials. The agency defines an adverse event as "any undesirable experience associated with the use of a medical product in a patient."

PatientsLikeMe, which is based in Cambridge, Mass., is a portal that allows people to share information and data about treatments, symptoms and side effects with other patients who are dealing with the same disease. With 350,000 users logging 28 million data points on more than 2,500 conditions, the site bills itself as the largest digital patient community in the world. The company has already collected data on 110,000 adverse events from 1,000 medicines that the FDA will now be able to access, according to a statement.

Currently, the FDA requires drug manufacturers to report adverse events only if they are made aware of a bad reaction to a drug that they produce. Patients and doctors may also voluntarily submit reports if they notice an unusual side effect. The FDA received over a million reports for adverse events from medicines in 2013. These events were said to have caused just over 118,000 deaths, though the FDA does not require proof of any connection to file a report and those reports also include instances when a patient took the wrong medicine instead of having a reaction to a medicine that was prescribed to them or that they purchased over the counter.

PatientsLikeMe has worked on projects with the National Institutes of Health and the Centers for Disease Control and Prevention. Earlier this year, the company announced a research project with Biogen Inc. to determine whether a fitness tracker worn around the wrist could be used in conjunction with a smartphone app to monitor the activity level of patients with multiple sclerosis.