Google has announced that it won’t run ads anymore for dangerous “unproven or experimental medical techniques,” following what the company describes as a “rise in bad actors” marketing untested procedures like stem cell therapy, cellular therapy, and gene therapy, as originally reported by The Washington Post.

As The Washington Post notes, untested stem cell therapies have led to severe blindness for some patients. And while the FDA won a case back in June to shut down a single clinic in Florida, the entire field is still largely unregulated, and the science unproven.

Untested treatments won’t be allowed to advertise going forward

According to Google’s announcement, the new policy will bar both treatments with “no established biomedical or scientific basis” at all, as well as ones with “insufficient formal clinical testing to justify widespread clinical use.” While Google hasn’t provided details as to what exactly the spike in dangerous ads looks like in more concrete, numerical terms, the company says that the ads have “no place on our platforms.”

While Google specifically calls out stem cell therapy and other similar forms of treatments, the new policy would seem to apply to all untested treatments, not just these specific fields. That said, the new policy does put Google, once again, in the role of ultimate arbiter over its platforms, left to decide on its own terms what does or doesn’t constitute “unproven or experimental medical techniques,” and which ads will be moderated, a role that the company has struggled with in the past (particularly when it comes to YouTube).

Google will still allow ads to promote research, along with clinical trials, so long as they follow the rest of the rules in Google’s health care and medicine advertisement policy. The company also notes that it will continue to evaluate ongoing research and will continue to revise its policies as needed in the future.