Scott Gottlieb's resignation as the Food and Drug Administration's (FDA) commissioner surprised biopharma investors. Gottlieb's legacy of holding tobacco companies accountable and battling opioid manufacturers is notable, but his other achievements, including accelerating drug review times and streamlining guidance for next-generation gene therapies, were also important. The high-profile departure creates uncertainty among investors, so let's take a closer look at Gottlieb's time running the FDA and what could be next for the drug industry.

A vocal advocate

An industry insider, Gottlieb brought with him to the FDA valuable experience that he leveraged to reshape the agency's policies on opiates.

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In an official statement on Oct. 30, 2017, he wrote, "One of my highest priorities as the Commissioner of the U.S. Food and Drug Administration is to take whatever steps we can to reduce the scope and human tragedy created by the epidemic of addiction to opioids."

It wasn't simply lip service.

Only weeks after Gottlieb's being sworn in as the FDA's 23rd commissioner, the FDA asked Endo International to stop selling Opana ER, an extended-release opiate, based upon the determination that its benefit "may no longer outweigh its risks." The drug was being manipulated to allow it to be injected, which was contributing to addiction and other health risks, including increasing the risk of spreading HIV and hepatitis C.

Gottlieb issued guidance to encourage generic-drug makers to develop alternatives to expensive, brand-name opioids that are specifically designed to limit their risk of abuse. He advocated against stigmatizing opioid addiction. Under his leadership, the agency approved a long-acting treatment for moderate to severe opioid use disorder, and it encouraged drugmakers to develop more innovate addiction treatments. He expanded the risk evaluation and mitigation strategy requirements for extended-release opioids to immediate-release opioids. He called for more training of healthcare providers on managing pain in patients. He put online sellers of illegal, unapproved, and misbranded opioids, including tramadol and oxycodone, in the crosshairs. And earlier this year, he said the FDA would begin implementing new packaging requirements that may better match the number of opioid doses to a patient's need. He also said the FDA was exploring ways to make Narcan-like products available over the counter to reduce death caused by addiction.

Check out the latest earnings call transcript for Endo International.

Opioids weren't Gottlieb's only target, though. He also took aim at tobacco companies and e-cigarette and vaping companies. For example, on March 4, he said e-cigarette use among children was at "epidemic levels." He targeted companies using kid-friendly marketing and flavors for their bad behavior, cracked down on stores for selling to minors, and instituted new studies to evaluate risks.

Gottlieb was also a big supporter of innovation. During his time at the FDA, it developed new regulatory frameworks for technology-specific and disease-specific innovations. He oversaw the approvals of the first gene therapies for cancer and blindness and an approval of a comprehensive genetic screening test for cancer patients. The first cancer drugs addressing the genetic makeup of the cancer, rather than its location, were also given the green light.

He advocated to support follow-on innovations that could boost competition to help crimp costs. The agency approved the first biosimilars -- lower-cost alternatives to high-priced specialty drugs -- on his watch too. Overall, his goal to speed the FDA's review of drugs contributed to the approval of 46 new therapies in 2017 and 59 new drugs in 2018, a record high. He also laid groundwork for new trial designs that could foster even faster drug development and approvals in the future.

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Now what

Gottlieb's success in holding drug companies accountable, while also spearheading innovation, was refreshing. Will his successor be as vocal a critic of opioid drugmakers and tobacco companies? Will they be as comfortable changing the FDA's long-standing practices and processes? Or will the FDA take a slower, more traditional approach from here on out? Until a new commissioner is named, biopharma and medtech stocks will probably become more volatile as stakeholders debate the pros and cons of potential replacements. That volatility could create buying opportunities, especially in companies working on next-generation treatments, but that will depend on how much the next FDA commissioner shares Gottlieb's vision. Therefore, investors should expect uncertainty until a new person's in charge of the FDA.