BALTIMORE — Federal scientists from the National Institute of Standards and Technology have identified a combination of substances believed to be responsible for a last week’s mass overdose in Baltimore’s Penn North neighborhood.

Lab testing revealed the presence of the following drugs in samples tied to the July 10 overdose event:

—Fentanyl, a highly potent synthetic opioid.

—Acetaminophen, a common pain and fever reducer.

—Caffeine, a central nervous system stimulant.

—Mannitol, an osmotic diuretic often used as a cutting agent.

—N-methylclonazepam, a benzodiazepine derivative with powerful sedative properties.

—Quinine, a compound historically used to treat malaria, now sometimes found as a drug adulterant.

The institute said that according to data from Maryland’s Rapid Analysis of Drugs program, most of these substances — including acetaminophen, caffeine, fentanyl, mannitol and quinine — are commonly found in the state’s illicit drug supply.

However, N-methylclonazepam has not previously been detected in Maryland through RAD, nor has it appeared in data from NIST’s Rapid Drug Analysis and Research, or RaDAR, program.

The intense sedative effects of N-methylclonazepam are consistent with reports from first responders in Penn North. Many individuals remained unconscious after receiving naloxone, a drug that combats the effect of opioid overdoses, suggesting the presence of a nonopioid sedative, federal scientists found.

The mass overdose sent at least 27 people to hospitals within hours.

Based in Montgomery County, NIST collaborated with the investigation through RaDAR, the agency confirmed to The Baltimore Sun. The institute used advanced technology to identify the drugs and cutting agents involved in the overdoses, which authorities have described as a possible “bad batch” of street narcotics.

“We identify all the drugs, cutting agents, and adulterants we can,” said Edward Sisco, the lead researcher on the project, through an email from a spokesperson. “If we find something new in the sample, we do additional testing to try to identify it.”

The RaDAR program relies on a technology called DART-MS, or direct analysis in real time mass spectrometry, that allows scientists to test drug residues — including swabs from used paraphernalia and empty baggies — rapidly and with high precision.

The goal of RaDAR is to monitor the chemical makeup of the illicit drug supply in near real time to help public health and law enforcement officials respond swiftly to emerging threats, according to NIST.

“Although this is part of an ongoing project, we are obviously working intensely right now to analyze samples from Baltimore as quickly as possible,” NIST spokesperson Rich Press told The Sun. “Our current turnaround time is less than 24 hours.”

The Drug Enforcement Administration is also assisting the Baltimore Police Department in the criminal investigation, which so far has not led to any arrests directly tied to the overdoses in Penn North, police have said.

Officials with the mayor’s office and the Baltimore Department of Health could not be reached for comment.

Over the weekend, however, Baltimore Police did arrest five people on narcotics charges near the site of the overdoses, describing the area as an open-air drug market.

Police have also been increasing surveillance in known drug-dealing hot spots across the city. Court documents suggest authorities are focusing on tracing the source of the dangerous batch that caused the outbreak of overdoses.

The RaDAR program began as a pilot in Maryland in 2021 and has since expanded nationally. NIST now analyzes between 750 and 1,000 samples monthly from 15 states.

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