D.C. Police Chief Cathy Lanier speaks at a news conference Monday as Mayor Muriel E. Bowser looks on. (Bill O'Leary/Washington Post)

D.C. Mayor Muriel E. Bowser vowed Monday to crack down hard on suppliers of synthetic drugs after a spike in overdoses sent dozens to area hospitals in the past month.

Bowser plans to introduce emergency legislation this week that would give the D.C. police chief authority to shut down any business found selling the drugs for a period of 96 hours while police investigate.

The legislation would also institute a “two-strike rule,” allowing the police chief to shut down any two-time offenders for a period of up to 30 days, coupled with a $10,000 fine — five times as much as the current penalty. The District’s Department of Consumer and Regulatory Affairs would then move to permanently revoke a store’s license, Bowser said at a Monday news conference outside the Sasha Bruce Youthwork, an organization that works with at-risk and homeless youths.

Speaking alongside Bowser, D.C. Police Chief Cathy Lanier said the new penalties would resonate with business owners in a way that previous measures have not.

“It’s not the cost of doing business anymore,” Lanier said. “You can’t just sell it for cash and get a slap on the wrist, because a 96-hour shutdown is significant.”

The drugs have also grown deadlier — a shift that the chief of the D.C. Department of Health, LaQuandra Nesbitt, said had spurred officials into action.

Officials have struggled for years to enforce the illegality of synthetic drug sales as manufacturers adjust rapidly to legislation and alter the chemical compositions of the drugs.

Newer incarnations of the drugs — previously referred to as “synthetic marijuana” for their mimicking of marijuana’s effects — produce symptoms that more closely resemble the hallucinogen PCP, officials said.

“When synthetic marijuana hit the market, it was more likely to make you euphoric. Now it’s making you more likely to be psychotic or hallucinate,” Nesbitt said at the news conference.

Lanier said that shift has caused some users to behave violently.

“We have had homicides that were carried out by persons high on those synthetic drugs and didn’t recall what happened,” Lanier said.

The drugs can often be found at local liquor stores or gas stations, marketed under names like Scooby Snax or K2, and are primarily used by young people.

“Synthetic drugs: Don’t be fooled by the names they’re marketed by, and don’t be fooled by people calling it an equivalent to marijuana,” said Bowser, who said the drugs represented “a clear and present danger to the public.”

The legislation is one of a couple of new measures that city officials announced in recent days to mark a shift in the District’s approach to fighting crime, and specifically drugs, in a changing environment.

Last week, D.C. police said it was dissolving its seven-member vice squads and instituting a centralized Narcotics and Special Investigations Unit in its place. A second group, the Criminal Interdiction Unit, which started work Monday, will work in coordination with the central unit to go after suppliers on the ground.

At Monday’s news conference, officials said the strategy shift reflected a reality on D.C. streets, where drug dealers have moved away from the open-air drug markets that characterized the crack epidemic of the 1980s and ’90s, and into a more sophisticated trade of synthetic drugs via licensed retailers and the Internet.

D.C. Council member Yvette Alexander (D-Ward 7), who flanked Bowser along with two other council members and city officials Monday, said that sales of the drugs had become so “blatant” in Ward 7 that some residents might believe them to be legal.

Alexander said that she, personally, was able to purchase synthetic drugs from a local store. But she promised that that was about to change.

“I’m giving fair warning to my businesses in Ward 7: I’m coming down to get you. And I’m going to send the chief out, because I know where you are,” she said.

Freshman council member and Bowser ally LaRuby May (D-Ward 8) echoed Alexander’s threats, telling business owners in her ward: “We’re going to shut you down. We’re going to make sure you no longer exist.

“If you don’t want to be a good neighbor, if you don’t want to be a good business in Ward 8, then you should start looking in the county or somewhere else,” May added.

On Monday, Bowser also said that the D.C. Department of Health was working to set up a system through which hospitals can be prepared to test patients showing symptoms of synthetic drug use and report synthetic drug-related emergency room visits to the police.

“This will allow us to know exactly what materials manufacturers are including in these lab-manufactured drugs,” she said.