NEW YORK (CBSNewYork) — Someone dies of a drug overdose every seven hours in New York City, health officials say.

In an effort to curb those deaths, the city wants to warn drug users about cocaine that has been laced with fentanyl.

Fentanyl is an opioid that’s 30-50 times more potent than heroin, according to the Department of Health.

“People who may use cocaine occasionally may be at risk of an opioid overdose,” the department said in a press release.

ICYMI: We’re warning patrons of bars/nightclubs on the Lower East Side about the dangers of cocaine laced with fentanyl: https://t.co/pGHPzrvBRz #HealingNYC pic.twitter.com/iF0XCTdzrA — nycHealthy (@nycHealthy) May 27, 2018

The health department said in 2016, fentanyl was found in 37 percent of overdose deaths involving cocaine — up from 11 percent in 2015.

So officials have been visiting bars and clubs on the Lower East Side to spread the word. They’ve been passing out free coasters warning about fentanyl-laced cocaine. The coasters include some safety tips, including to use cocaine with others, so that in the event of an overdose there’s someone who could help. They also urge users to carry naloxone or narcan, which can reverse an overdose.

Users can call 311 to find out where to get naloxone. For treatment, users can call 888-NYC-WELL.

CBS2’s Andrea Grymes asked Mayor Bill de Blasio if he thought this would encourage cocaine use.

“When the health department tries to figure out a public health campaign, they are very mindful of not wanting to have unintended consequences,” the mayor replied. “But, let’s be blunt, tragically there’s a lot of people using cocaine and thinking it’s safe… Any way to tell people it’s not safe anymore and could be laced with an extraordinarily lethal drug — that’s our obligation to get that information out.”

The health department said research proves this type of messaging does not encourage drug use. A spokesperson said the campaign is about meeting people where they are.

“The city is not encouraging drug usage — we are encouraging safety,” officials said in a statement. “We can’t connect New Yorkers to treatment if they are dead.”

The program also includes Narcan training for bar and club staffers.

The health department said it chose the Lower East Side for the campaign, because of its high number of bars and nightclubs, but noted it’s a city-wide problem.