For decades, the pharmaceutical industry has operated under an understanding so elegant it was almost too good to be true: Tell television viewers about the most serious risks of your arthritis medication, and then cheerfully direct them to a website or toll-free number for the rest. The rest, of course, could run to several pages of fine print that no one would ever read.

Now the Food and Drug Administration is proposing to end that arrangement.

The agency has put forward a rule that would eliminate the so-called adequate provision guidance, which has allowed drugmakers to keep their broadcast advertisements relatively brief by outsourcing the complete litany of side effects and contraindications to other sources. Under the proposed change, all of that information would need to appear in the advertisement itself.

The implications for the thirty-second spot are not difficult to imagine.

"I look at this as a backdoor, or de facto, ad ban," said Jim Potter, executive director at 4As Health, the pharmaceutical marketing arm of the American Association of Advertising Agencies.

Mr. Potter said he was not surprised by the proposal. Last September, the Trump administration released a memorandum outlining its intention to crack down on direct-to-consumer pharmaceutical advertising, with Robert F. Kennedy Jr., the secretary of health and human services, leading the effort. (Mr. Kennedy has long been a critic of the pharmaceutical industry, though his concerns have not always aligned with those of the F.D.A.)

"This is one of Secretary Kennedy's campaign promises," Mr. Potter said.

The agency, for its part, argues that requiring complete safety information in advertisements would benefit patients by improving their understanding when making health care decisions. The industry's counterargument is more succinct: the entire ad would become risk information.

The rule is far from final. The F.D.A. must still publish it as a formal notice, allow for public comment, and conduct months of review — a process that typically takes about two years. Legal challenges invoking First Amendment protections for commercial speech are considered likely.

"There's a long history of the F.D.A. being smacked down in the courts," noted one regulatory expert.

In the meantime, Mr. Potter has advice for his members: "Put some money away for next year for a legal challenge. This looks real now."

Whether it looks real on television remains to be seen.

Original story published in campaignlive.com: "FDA takes first step toward ‘de facto’ ad ban: What to know | Campaign US"