By: Staff Writer
March 31, 2026
A recent study from the journal Environmental Pollution indicates that about one third of the sharks sampled in their study have tested positive for some contaminant like cocaine or caffeine, raising concerns for marine biologists and the changing nature of sharks.
The report indicated that of the 85 analyzed sharks, 28 individuals exhibited detectable levels of four contaminants of emerging concern (CECs): acetaminophen, diclofenac, cocaine, and caffeine. All other compounds were below the limit of detection (LOD) in the analyzed samples. Detections were restricted to three species: Reef shark, Nurse Shark, and Lemon Shark.
“We’re talking about a very remote island in the Bahamas,” study co-author Natascha Wosnick, a biologist with the Federal University of Paraná in Brazil, told a media outlet.
The effect of the drugs on shark behaviour and levels of aggression is yet to be fully explored, said Wosnick. Research on goldfish suggests caffeine increases their energy and focus. Some reports have highlighted unusual shark behaviour in the region, including a normally reclusive hammerhead captured on camera during Shark Week, appearing to target divers.
It also remains unconfirmed how and where the creatures are consuming the drugs, though sewage pollution and human behaviour are being held up as the likely causes. Some have blamed hard-partying tourists in the region, while local fishermen claim to have witnessed sharks biting into packets of cocaine thrown overboard by drug smugglers.
Medications, illicit drugs and other substances are “increasingly recognized as contaminants of emerging concern” in oceans and other bodies of water, the researchers said. They noted areas that are “undergoing rapid urbanization and tourism-driven development” are especially at risk. This is the first study looking at the effect of these contaminants on sharks in the Bahamas, the researchers said.
“While the detection of cocaine — an illicit substance — tends to draw immediate attention, the widespread presence of caffeine and pharmaceuticals in the blood of many analyzed sharks is equally alarming,” added Wosnick.
One shark — a baby lemon shark in a nursery creek — tested positive for cocaine. The amount was far lower than what researchers previously found in sharks off Brazil, but that earlier study examined muscle tissue, not blood. Because drugs persist longer in muscle, their presence in blood points to recent exposure. Wosnick says the shark may have ingested a packet containing cocaine residue; she’s seen such packages near that creek before. “They bite things to investigate and end up exposed” to substances, she says.