'Suwon drug zombie' mystery deepens as National Forensic Service tests come back negative

A man in his 30s dubbed the "Suwon drug zombie" on social media has tested negative in all precision drug analyses conducted by the National Forensic Service, despite having tested positive for methamphetamine in a rapid field test at the time of his arrest. Experts say the discrepancy is likely due to cross-reactivity — when a rapid test reacts to substances chemically similar to the target drug — but have not ruled out the possibility that the man used a novel drug that current tests cannot detect.

The Suwon Gwonseon Police Station is investigating the man on charges of violating the Narcotics Control Act. He has been unable to give a consistent account of the behavior captured in widely circulated social media videos, police said. His hair sample has been sent to the National Forensic Service for additional analysis.

The man has reportedly changed his explanation multiple times for why he was seen bending his body at an abnormal angle with his arms hanging limply. He has variously said he was stretching, that he was feeling unwell, and that he cannot remember what happened.

A video showing the man standing in an unusual posture at an unspecified location in Suwon spread widely on social media June 22, immediately prompting suspicions of drug use. Police tracked him down and arrested him on charges of violating the Narcotics Control Act. A rapid field test returned a positive result for methamphetamine, but a preliminary drug analysis the National Forensic Service conducted June 24 came back negative, leading police to release him and continue the investigation without detention. A subsequent precision urine analysis also returned a negative result.

Why did the tests produce conflicting results? Experts point to the inherent limitations of rapid field testing. Such tests can react to substances chemically similar to the target drug — a phenomenon known as cross-reactivity.

Jang Hyeong-min, chief executive of Innorixon, a company that imports drug testing kits, said ephedra — an ingredient found in some traditional herbal medicines — can trigger a positive methamphetamine result in a rapid field test. "If someone is taking an herbal remedy containing ephedra and undergoes a rapid test, it can come back positive for methamphetamine," he said.

Ephedra is not a controlled substance, yet it registers as methamphetamine in rapid tests. The same is true of phentermine, an appetite suppressant. Some cough medicines can also produce a false positive for opioids.

An official from the National Forensic Service's narcotics division said rapid field tests are best understood by analogy with COVID-19 home test kits. "Just as people used rapid kits during the pandemic and then went to a hospital for a definitive result, a rapid drug test is simply a quick tool for identifying suspicious circumstances — not a conclusive finding," the official said.

The National Forensic Service conducts two further stages of testing for greater precision: a preliminary analysis and a full precision analysis. The preliminary stage uses an antigen-antibody reaction. "It involves attaching a protein that can bind to the suspected drug component and then checking for chemical bonding to assess similarity," the official said. Cross-reactivity remains possible at this stage, however, so an additional precision test follows.

The precision analysis uses mass spectrometry — a method that exploits the fact that each substance has a unique mass value — to determine whether any mass values corresponding to controlled substances are present in the sample. The margin of error at this stage is extremely small, the National Forensic Service official said.

One exception involves novel drugs the National Forensic Service has not yet catalogued, which can evade detection even in precision testing. "It is not a common scenario, but blind spots can exist," the official said. "When a novel drug or unknown substance is detected, we analyze it quickly and share the findings. The National Forensic Service responds very rapidly by international standards as well."

Police said they are keeping all possibilities open as the investigation continues. "We are looking at this from multiple angles, including the man's everyday lifestyle and whether he takes any medication for health reasons," a police official said.