Relationship status: "It's Complicated."

Facebook and the pharmaceutical industry have had an uneasy partnership in recent years. Many drug companies didn't even join the site until Facebook gave them a privilege that others do not have - blocking the public's ability to openly comment on a page Wall.

But that's about to change.

In a reversal by Facebook, most drug company pages will have to have open Walls starting Monday.

Companies are worried that open Walls mean open risks, and many are reconsidering their engagement on Facebook.

AstraZeneca shut down on Friday a page devoted to depression - the company sells the antidepressant Seroquel. Johnson & Johnson said it will close four of its pages on Monday. Other companies said they will monitor their pages more closely.

The industry is concerned that users might write about bad side effects, promote off-label use or make inappropriate statements about a product. Aside from poor word of mouth, the comments could raise concerns from government regulators.

Facebook will not say what specifically prompted its change of heart. Andrew Noyes, manager of public policy communications for Facebook, said in an email, "We think these changes will help encourage an authentic dialogue on pages."

Facebook will allow companies to continue to block Wall comments on specific prescription product pages, but those are a minority of pharmaceutical company pages. Most pages - soon to be open - are focused on companies themselves or on disease or patient-specific communities, which then have ties to the companies' prescription products.

Johnson & Johnson will shut down two pages focused on attention deficit hyperactivity disorder -ADHD Allies and ADHD Moms - along with pages focused on rheumatoid arthritis and psoriasis. Combined, the four pages have more than 40,000 "likes" - people following the page and its updates. Johnson & Johnson sells the ADHD drug Concerta, psoriasis drug Stelara and arthritis drugs Simponi and Remicade.

Facebook has become an increasingly popular destination for patient communities, with many shifting over the past couple years from message boards and other websites to pages like those hosted by companies, said Lisa Gualtieri, an assistant professor at the Tufts School of Medicine who studies social media and health.

Jonathan Richman, a group director for the marketing agency Possible Worldwide, said that companies are exaggerating the risks of an open Wall, and he is trying to persuade them to stay online.

The industry "nightmare" is processing of adverse event reports (AERs), said Joe Farris, co-founder of the Digital Health Coalition, a nonprofit group focused on online marketing of health-care products. Users might write on a company's Wall about a specific product causing an unexpected reaction or injury. That information could qualify as an AER, and it must then be filed with the Food and Drug Administration, which uses the reports to monitor product safety.

Richman said that a flood of AERs is unlikely. "I don't think we're going to see a change in consumer behavior overnight."

Companies also have ways of circumventing at least some of the problems of an open Wall. Page owners, like any other Facebook user, will be able to delete comments from their pages once they appear, though that could mean 24-hour monitoring by the company itself or a third party.

Pfizer, for example, will keep its current pages online and "monitor to make sure no inappropriate comments are posted, and manage them if and when they occur," said Andrew Widger, a company spokesman.

Amgen will maintain its "Breakaway From Cancer" page, said spokeswoman Mary Klem. Amgen sells the cancer drugs Neulasta, Neupogen and Vectibix.

Sanofi also has no plans to remove its pages from Facebook, said spokesman Jack Cox. The company runs a diabetes page with more than 1,500 likes and makes the insulin products Apidra and Lantus. According to Dennis Urbaniak, Sanofi's U.S. vice president for diabetes, Facebook has become more than a marketing and branding tool.

"We've been able to get feedback that's more genuine and relevant," Urbaniak said. "We see (the page) as a way of getting to know patients better." To avoid problems, the company avoids discussion of specific products and sets up "clear terms and conditions with the user" on its page, which also features safety information for its diabetes products.