Mouse experiments with the popular club drug ketamine may be skewed by the sex of the researcher performing them, a study suggests. The findings only deepen the mystery of how ketamine, which has powerful mood-lifting properties, interacts with the brain. They also raise questions about the reproducibility of behavioral experiments in mice.

Ketamine is best known as a psychoactive recreational drug. But it has caught psychiatrists’ interest because of its potential to treat depression within hours. It’s unclear exactly how the drug works, however, and many researchers are using animal models to suss out the mechanism.