Many women notice that their mood changes around times of hormonal fluctuation — before a period, after having a baby, or during the perimenopause. For some, these changes are mild; for others, they can be life-altering. This pattern is increasingly recognised as a distinct form of depression known as reproductive depression. Here, I explain what that means, why hormones can influence the brain so profoundly, and how this understanding is helping us shape more effective, personalised treatments.