Subtle, but seismic: That’s how experts describe the impact on health care of the U.S. Supreme Court’s recent decision in Loper Bright Enterprises v. Raimondo. That ruling overturned a decades-old legal doctrine known as Chevron deference.

The decision brings sweeping change to a wonky corner of the regulatory universe. Previously, courts deferred to federal agencies’ deep expertise to interpret legal gray areas. The court’s new ruling wrests that power back. This deep-in-the-weeds decision applies to all the federal agencies that make decisions affecting our health, including the Food and Drug Administration, the Centers for Medicare & Medicaid Services, the Environmental Protection Agency, and more.

The consequences could take years to emerge. Chevron deference wasn’t about a specific law, but rather how statutes are put into action. When a law passed by Congress is ambiguous — and when it comes to health policy, so many necessarily are — Chevron deference instructed the courts to let agency experts figure out how to interpret it.

Shifting that responsibility from scientists to judges is terrible for the health of the nation. It has the potential to undermine everything from bread-and-butter decisions made by the FDA to health agencies’ ability to act swiftly in the face of an emergency.

To be clear, the decision doesn’t result in some immediate dismantling of agency power. “It’s not like a categorical light switch,” says Nicholas Bagley, an expert in administrative law and health law at the University of Michigan. “It’s more of an intensification of judicial oversight.”

In fact, Bagley expects the outcome of most cases to be the same as before the Chevron decision. But the specter of uncertainty is powerful. It can embolden people to bring lawsuits that previously might have had little chance of success, while at the same time weakening an agency’s resolve to enact new regulations or experiment with innovative projects to improve public health.

Manufacturers, in turn, are left not knowing the rules of the road, says Joseph Ross, a professor of medicine and public health at Yale School of Medicine, who submitted an amicus brief on behalf of the government in the case. Predictability is central to the drug industry, whether that’s understanding how to meet the FDA’s expectations or how Medicare decides what products it will pay for. The new ruling “has the potential to sew a lot of chaos,” Ross says.

To understand the scope of the problem, consider the language in the Federal Food, Drug & Cosmetic Act that lays out the agency’s standards for approving a drug. The law requires a company to offer “substantial evidence” in the form of “adequate and well-controlled” studies, conducted by “experts qualified by scientific training and experience to evaluate the effectiveness of the drug.”

“It’s just dripping with ambiguity,” says Holly Fernandez Lynch, a professor of medical ethics and health policy at the University of Pennsylvania’s Perelman School of Medicine. “What’s an adequate trial? What’s a well-controlled trial? What’s an expert?”

Even more fundamental, what counts as a “disease” or a “drug”? The ambiguity of those words could be used to evade the FDA’s purview. For example, anti-abortion groups already argue that pregnancy is not a disease, so the FDA shouldn’t have oversight of medicines used for abortion or even birth control. Already, vaping manufactures see an opening to challenge the agency’s crackdown on flavored e-cigarettes.

The potential for interpretation opens the door to a rash of lawsuits — but over what and by whom is still an open question. “Traditionally, we just haven’t seen people taking runs at the FDA on drug authorization,” Bagley says. The prominent outlier has been conservative groups’ recent challenge to the agency’s approval of mifepristone, which in combination with misoprostol is used both to treat miscarriages and to induce abortions. In 2022, a group of antiabortion organizations and doctors challenged the FDA’s assessment of its safety, a case that the Supreme Court dismissed on a technicality last month.

“What we don’t know is whether the mifepristone case augers a new era in which there’s going to be some efforts to bring these kinds of challenges, or whether that’s just a case about abortion politics and has no lasting significance for the industry,” Bagley says.

Still, there’s reason to worry about the broader context of the case. The Supreme Court turned back the mifepristone challenge based on standing — that is, the judges said the plaintiffs were not being injured by the drug’s approval and so did not have a right to challenge it. Yet we’re also seeing some judges expand the definition of who is allowed to bring a case which, combined with the wiggle room created by the overturning of Chevron, could open the door to more second-guessing of the FDA’s decisions. And it’s worth noting that in a separate case this term, Corner Post v. Federal Reserve, the court gave plaintiffs a lot more time to sue regulatory agencies.

Taken together, this could all make it easier for conservative groups to challenge other drugs or vaccines they find controversial.

Large pharmaceutical companies are probably unlikely to sue over, say, a drug’s failure to pass muster — they are unlikely to want to risk the relationship needed to get their products to market. But there’s still plenty of room for gadflies to make trouble. Consider a small company whose future relies on one make-or-break drug. If the FDA declines to approve it, they might feel a lawsuit is worth the gamble.

But the larger worry is that the ruling becomes an albatross around the agency’s neck. That weight could take the form of frivolous lawsuits, but it also could look like a growing reluctance to pursue innovative efforts.

Health agencies are already overly cautious before taking a step toward implementing a new regulation. “Now, the knowledge that it’s going to precipitate more litigation challenges is going to doubly chill regulatory efforts to address things as and when they arise,” says Andrew Twinamatsiko, director of the Health Policy and the Law Initiative at Georgetown’s O’Neill Institute. For example, regulators ideally would step in to set clear boundaries for the rapid proliferation of artificial intelligence in health care. But they might hesitate to act in real time, or water down their approach, to avoid being bogged down in lawsuits.

The FDA is remarkably small considering the breadth of the economy that it touches, Ross notes. That means the agency must be efficient with its resources, something that requires working with the confidence that its expertise is trusted. The threat of being constantly second-guessed could cause it to be far more cautious. “The consequences are often going to be hidden,” Ross says, who worries about all “the stuff that we don’t see, that regulators no longer feel comfortable doing.”

That’s not great news for industry, which thrives on regulatory certainty, and it’s not good for health care consumers, who might not even know what they’re missing.

Lisa Jarvis is a Bloomberg Opinion columnist covering biotech, health care and the pharmaceutical industry.