WASHINGTON – Food and Drug Administration Commissioner Scott Gottlieb, who stood out in the Trump administration for his efforts to increase regulations around youth vaping and tobacco – efforts that drew criticism from some of the president's conservative allies – surprised supporters and critics with his resignation on Tuesday.

Gottlieb, a physician and a venture capitalist who was sworn in as FDA commissioner in May 2017, will leave his position in one month, the Department of Health and Human Services said. No successor was named Tuesday.

Gottlieb, 46, took aggressive steps to curb youth vaping, which he declared an "epidemic" last year, and opioid addiction.

In November, citing a rise in youth vaping that he called "discouraging," he unveiled plans to sharply restrict sales of sweet-flavored electronic cigarette liquid at convenience stores. His proposed regulatory changes have not yet been implemented.

Gottlieb's efforts drew praise from consumer watchdog groups that had called for aggressive steps to stem the unfavorable youth vaping trends.

Matthew Myers, president of the Campaign for Tobacco-Free Kids, said Gottlieb's work is incomplete.

"He initiated a number of potential actions that would have made an extraordinary impact, but he leaves with those actions unfinished," Myers said. "On e-cigarettes, he deserves credit for shining a spotlight on the crisis of youth e-cigarette use. It will be impossible to reverse that crisis unless the FDA adopts industry-wide rules before he leaves.”

Free-market groups and vaping industry interests have been critical of the FDA efforts under Gottlieb. Jeff Stier is a senior fellow at the free-market think tank Consumer Choice Center.

"We’ve been complaining and pointing out how the administration’s approach to e-cigarettes is not consistent with what president promised on limited regulation,” he said. “What Gottlieb was threatening was over-regulation."

Gottlieb predicted the criticism his proposals would draw.

“Everything that we're thinking about is requiring a very careful balancing where there are going to be accommodations that we have to make, there’s going to be critics on both sides,” he told USA TODAY's editorial board in November. “There's many people who say we went too far and people who say we don't go far enough.”

Gottlieb said Tuesday he was "immensely grateful for the opportunity to help lead this wonderful agency," and for the "strong support" of President Donald Trump and Health Secretary Alex Azar.

"This has been a wonderful journey and parting is very hard," he tweeted.

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Trump tweeted that Gottlieb had "done an absolutely terrific job" as commissioner: "He and his talents will be greatly missed!"

Azar called Gottlieb "an exemplary public health leader, aggressive advocate for American patients, and passionate promoter of innovation."

"Scott’s leadership inspired historic results from the FDA team, which delivered record approvals of both innovative treatments and affordable generic drugs, while advancing important policies to confront opioid addiction, tobacco and youth e-cigarette use, chronic disease, and more," Azar said in a statement. "The public health of our country is better off for the work Scott and the entire FDA team have done over the last two years.”

Gottlieb previously served as the agency's deputy commissioner for medical and scientific affairs.

Stier said Gottlieb's efforts against e-cigarettes “diverged and diverged dramatically” from the Trump administration's pledges to limit regulations. When Stier and others realized that Gottlieb had Azar's support on vaping, Stier says, they shifted their attention to the White House.

A coalition of more than one dozen conservative groups, including Americans for Tax Reform and FreedomWorks, appealed to the White House to intervene to halt Gottlieb’s e-cigarette vaping product restrictions.

In a letter last month, the groups argued that escalating teen vaping rates had led to "regulatory panic and significant government overreach." They urged Trump to "pump the brakes" on the FDA's proposed regulations.

John Walters, now chief operating officer at the Hudson Institute, directed the Office of National Drug Control Policy during the George W. Bush Administration while Gottlieb worked at the FDA.

For a physician, Walters said, trying to balance administration views on regulations and taxes against public health and science could be particularly challenging.

“You want to reflect some of those principles," Walters said. "But you also know, acutely as he does, that physicians can really kill people and make their lives worse."

Gottlieb spoke passionately about the risks of vaping.

"Teenagers are becoming regular users, and the proportion of regular users is increasing," he told USA TODAY last year. "We’re going to have to take action. ...

"No one can look at the data and say there’s no problem."

Soon after he became commissioner, he told a conference at the National Academy of Medicine that he didn't want to repeat what he described as the mistakes made when he was at the agency in the 2000s, when the government could have regulated opioids more closely.

Walters notes there was considerable pressure from the powerful drug industry to not overregulate opioids, just as there is from “the sale of these vaping devices."

"There’s considerable money that’s promised to be made," he said.