In 1965, Schildkraut et al. came up with that the hypothesis that mental illness as depression would be due to a chemical imbalance and deficiencies in neurotransmitters such as serotonin. Markus Sjöborg explores the reasons why this hypothesis is still prevalent in Sweden despite the fact that it has long been rejected in other countries. The piece is based on a research thesis in Medical History undertaken at Uppsala University in 2020. Read in Swedish or in an English translation.