Gottlieb’s measures against teen vaping are some of the FDA’s most high-profile moves since he joined in May 2017. On the heels of recent research indicating that almost 40 percent of American high-school seniors vaped that year, the agency proposed guidelines that would take flavored e-cigarette cartridges out of most brick-and-mortar retailers in America, including convenience stores. Flavored vape products, the agency argued, were especially easy entry points for teen use, and they weren’t necessary in order for e-cigarettes to be used as effective alternatives to combustible cigarettes for adult smokers.

Read: The FDA’s mango-flavored trolley problem

That move was heralded as a step in the right direction by people such as Robert Jackler, a Stanford University professor who researches how e-cigarettes like the ultra-popular Juul are marketed to young people. Gottlieb’s plans to leave the agency worry him. “I hope that his successor shares a similar passion for protecting youth from nicotine addiction,” Jackler said in an emailed statement. “The upward spike in tobacco stocks is a worrisome sign that the industry anticipates relief from regulation.” Indeed, stocks for the tobacco giants Altria and British American Tobacco did inch northward after Gottlieb’s announcement yesterday, although no successor for Gottlieb’s role has been named.

Bonnie Halpern-Felsher, a pediatrics professor and tobacco-use researcher also at Stanford, feels similarly. “I am shocked and saddened by FDA Commissioner Gottlieb’s resignation,” she says. Although she emphasized that little is known about what’s to come at the agency, losing a strong advocate is always cause for concern. “I worry, since he has definitely been leading the way in proposing vaping regulation, recognizing and trying to reduce the youth-vaping epidemic,” Halpern-Felsher says.

Meanwhile, Gregory Conley, the president of the American Vaping Association, criticized Gottlieb’s lack of effort on behalf of small- and medium-size e-cigarette entrepreneurs. “We are hopeful that the next FDA Commissioner will undertake real efforts to repair our country’s broken nicotine regulatory system,” he said in a statement released on Twitter. Some conservatives have been critical of what they see as the current FDA’s overly meddlesome approach to vaping businesses, which they argue drives adult smokers away from alternatives that could save their life.

For Gottlieb’s part, he has continued to be outspoken, even after announcing his departure. In a live interview with The Hill on Facebook earlier today, he emphasized that his decision to leave the FDA was strictly out of a desire to spend more time with his family in Connecticut, and that he intended to put his last few weeks on the job to good use. “I am extremely confident that the policy that was reported on Friday will be out very shortly,” Gottlieb said, referring to rumors late last week that the FDA’s restriction on flavored vape cartridges had been turned over to the White House for final approval.