Oversulfated chondroitin sulfate is a contaminant in heparin associated with adverse clinical events.

Summary: When patients started having sudden, severe allergic reactions to the blood thinner heparin, scientists raced to find the cause. They discovered a "mimic" molecule hiding inside specific batches of the drug. Called oversulfated chondroitin sulfate (OSCS), this contaminant looks chemically similar to heparin, allowing it to sneak past standard safety tests. By using advanced high-resolution analysis, researchers identified the imposter’s unique structure. This discovery has led to new, stricter screening methods to ensure the heparin supply is safe and free from this dangerous contaminant.