BERLIN (AP) — The German hospital treating Russian dissident Alexei Navalny says tests indicate that he was in fact poisoned.

The Charité hospital said in a statement Monday that the team of doctors who have been examining Navalny since he was admitted Saturday have found the presence of “cholinesterase inhibitors” in his system.

Cholinesterase inhibitors are a broad range of substances that are found in several drugs, but also pesticides and nerve agents.

Doctors at Charite say at the moment the specific substance Navalny was exposed to is not yet known.

The hospital says “the patient is in an intensive care unit and is still in an induced coma. His health is serious but there is currently no acute danger to his life.”

“Alexei Navalny’s prognosis remains unclear; the possibility of long-term effects, particularly those affecting the nervous system, cannot be excluded,” wrote the hospital.

Navalny is being treated with the antidote atropine, according to the hospital.