Sharks off Eleuthera Island in the Bahamas have tested positive for a surprising mix of human drugs, according to a new scientific study. Researchers found traces of caffeine, common painkillers and even cocaine in blood samples taken from local sharks.

What the scientists did and what they found

The research was led by biologist Natascha Wosnick from the Federal University of Paraná and published on February 20, 2026 in the journal Environmental Pollution. Scientists sampled blood from 85 sharks near Eleuthera and discovered that almost one third carried traces of human-related substances.

Substances detected

  • Caffeine — the most common substance found and the first recorded occurrence in sharks globally.
  • Acetaminophen — identified in sharks for the first time.
  • Diclofenac — an anti-inflammatory drug detected in the Bahamas for the first time in sharks.
  • Cocaine — at least one shark tested positive.

Which sharks were sampled

  • Caribbean reef sharks
  • Nurse sharks
  • Lemon sharks

How these drugs likely reached the ocean

Researchers point to several human sources. Wastewater and sewage discharge are the primary suspects, especially where infrastructure is limited. Heavy tourism and related coastal activity can increase local pollution. Cocaine may also enter the water through lost or discarded shipments.

Signs of possible effects on shark health

Sharks that tested positive showed signs of metabolic shifts. The study found altered levels of triglycerides, urea, and lactate, changes that can indicate physiological stress. Direct behavioral effects on sharks were not confirmed by this study, but other fish studies suggest that stimulants such as caffeine can change energy use and responses to risk.

Wider context

This work builds on earlier findings. A 2024 study by the same research group off Rio de Janeiro recorded even higher cocaine levels, with every sampled shark testing positive. That earlier research raised questions about long term impacts on marine life and potential risks for people who eat seafood from affected areas.

Bottom line

The study highlights a clear point: human pollution is reaching even apex predators. Scientists say more research is needed to understand long term ecological and health consequences. For now, the presence of caffeine, painkillers and cocaine in sharks is a stark reminder that coastal and marine pollution can show up in unexpected places.