Studies using deuterium and heavy water have shown that they have negative effects on the immune system: an increased amount of deuterium in the body decreases the number of leukocytes in the blood and weakens the body's ability to respond to disturbing factors.

Experiments on rodents have shown that a deuterium concentration of 25% in body water causes sterility, because neither gametes nor zygotes can develop. High concentrations of heavy water quickly kill fish, amphibians and insects.

Small mammals, such as rodents, die after about a week if they drink heavy water. The cause of death is similar to that of cytotoxic poisoning (in the case of chemotherapy) or acute radiation syndrome.