The oestrogen protection hypothesis proposes that oestrogen has a protective effect against onset of schizophrenia. In support of this: Epidemiological studies have shown that young women are less likely to develop schizophrenia than men of the same age, and women are more likely to develop late-onset schizophrenia after menopause. Clinical studies have shown higher psychotic symptoms in perimenopausal women, and women at the low oestrogen phase of the menstrual cycle. Animal studies provide further evidence in support of the oestrogen protection hypothesis. Three randomised double-blind placebo-controlled trials and an open-label study showed that adding oestradiol to women's usual antipsychotic medications was associated with significant abatement of schizophrenia symptoms. A small study of men with schizophrenia who received oral oestradiol valerate also showed a significant abatement in psychotic symptoms. Although oestrogen appears to be a useful treatment for schizophrenia, further research is required to determine the correct dose and duration of use of oestradiol. New types of oestrogen compounds may provide a safer, non-feminising approach for the treatment of schizophrenia.