WASHINGTON, Sept 9 (Reuters) - The U.S. Food and Drug

Administration will send out around 100 cease-and-desist

enforcement notices and thousands of letters warning

pharmaceutical companies that direct-to-consumer ads must comply

with regulations that are already on the books, senior

administration officials said on Tuesday.

The FDA plans to enforce regulations stipulating that drug

ads not create a misleading impression about the products and

appropriately disclose side effects, the officials said.

"There are ads that are clearly crossing the line with

respect to the regulation, making any potential future legal

action, I think, pretty clear cut," one of the officials said.

U.S. President Donald Trump also signed a presidential

memorandum on Tuesday afternoon, the White House said, calling

on his administration to step up enforcement of

direct-to-consumer pharmaceutical ads in order to ensure

transparency and accuracy.

"The Secretary of Health and Human Services shall

therefore take appropriate action to ensure transparency and

accuracy in direct-to-consumer prescription drug advertising,"

the memorandum said.

The presidential action and FDA letters coincide with

the release of the report on U.S. children's health by U.S.

Health Secretary Robert F. Kennedy Jr.'s Make America Healthy

Again Commission.

The officials said that enforcement of drug ads has been

increasingly lax, adding that last year, the FDA did not send

out any enforcement letters about drug advertising.

They did not disclose which companies had been sent the

enforcement or warning letters. They said they were not only

concerned about ads from drugmakers, but also ads from online

pharmacies "that are not following the same rules that many

pharmaceutical companies follow."

The government is also examining the role social media

influencers play in advertising drugs and plans to close a

loophole that allows companies to refer patients to a website

for information on side effects, the officials said.

Administration officials said there are no additional

presidential actions planned on direct-to-consumer drug ads,

calling the memorandum "the strongest, boldest action that we

can take on making sure that patients have adequate safety

information."

In his first term, Trump attempted to push through a rule

that would have forced pharmaceutical companies to include the

wholesale prices of their drugs in television advertising.

U.S. courts sided with drugmakers Merck ( MRK ), Eli Lilly ( LLY )

and Amgen ( AMGN ) and struck down the rule.

U.S. pharmaceutical lobby group PhRMA said its member

companies "are committed to responsible advertising, and we look

forward to learning more details about the policy changes

announced today."