The U.S. Food and Drug Administration (FDA) aims to reduce nicotine levels in cigarettes, in a major regulatory shift announced on Friday that sent traditional cigarette company stocks plunging.

FDA Commissioner Scott Gottlieb outlined a package of measures the agency plans to explore, seeking comments as it explores ways to reduce the harmfulness of smoking. The federal agency has had the power since 2009 to cut nicotine levels but hasn't done so.

"Nicotine itself is not responsible for the cancer, the lung disease and heart disease that kill hundreds of thousands of Americans each year," he said. "It's the other chemical compounds in tobacco and in the smoke created by setting tobacco on fire that directly cause illness and death."

The FDA's move extends the timeline for applications for new e-cigarette clearance by the FDA to Aug. 8, 2022, giving e-cigarette companies more time to keep their products on the market before the agency goes into the process of final review. It also gives the FDA more time to set the proper framework for regulating e-cigarettes.

Gottlieb said the agency needs time to focus on nicotine regulation and not be distracted by the debate on whether e-cigarettes help smokers quit.

Campaign for Tobacco-Free Kids president Matthew Myers praised the overall approach as "bold and comprehensive" but called the e-cigarettes delay "a serious error."

"It's hard to overstate what this could mean for the companies affected: non-addictive levels of nicotine would likely mean a lot fewer smokers and of those people who do still light up, smoking a lot less," said Neil Wilson, a senior market analyst with ETX Capital in London, U.K.

"This is just the U.S. regulator acting, but we can easily see others, particularly in Europe, where regulatory pressures are already extremely high, following suit."

E-cigarettes allow users to choose the nicotine strength of their product.

According to the Quit Smoking Community, a typical cigarette has about 18 milligrams of nicotine. In contrast, an e-cigarette can contain anywhere between zero milligrams and 42 milligrams of nicotine. It depends on user preference.

The FDA's official media release specifically mentions that the agency plans on developing product standards to "protect against known public health risks, such as electronic nicotine delivery systems (ENDS) battery issues and concerns about children's exposure to liquid nicotine."

ENDS are devices like e-cigarettes and nicotine vaporizers.

The agency cannot reduce nicotine levels to zero, nor can it ban cigarettes, but Gottlieb said the FDA would study regulating nicotine levels in an attempt to make cigarettes less addictive.

The announcement sets in motion a lengthy rule-making process that will involve public comment and input from multiple stakeholders before any measures take effect.

For e-cigarettes, the agency extended the deadline by up to four years, and up to three years for cigar companies, to comply with a 2016 rule that gave the FDA oversight over the products, giving them more time on the market without regulation.