Why does a woman's mood improve the day she starts her period, particularly in those with premenstrual syndrome (PMS) or premenstrual dysphoric disorder (PMDD)?

Why Mood Improves at Menstruation Onset in PMS/PMDD

Mood improves when menstruation starts because the withdrawal of progesterone and its metabolites (particularly allopregnanolone) ends, terminating the hormonal instability that characterizes the luteal phase—it is the fluctuation and withdrawal pattern itself, not sustained hormone levels, that triggers mood symptoms in vulnerable women. 1, 2

The Core Mechanism: Hormonal Instability, Not Absolute Levels

The fundamental principle is that mood disturbances in PMS/PMDD are caused by sudden withdrawal, rapid fluctuations, and the pattern of hormonal changes—not by high or low absolute hormone levels. 1, 2 This explains the paradox of why symptoms resolve when hormones drop at menstruation:

• During the luteal phase, progesterone increases 10-fold and then rapidly withdraws before menstruation, creating the hormonal instability that triggers symptoms in vulnerable individuals 2, 3
• Women with PMS/PMDD show differential sensitivity to these normal hormonal fluctuations, meaning the same physiologic changes affect them differently than unaffected women 1, 2
• Once menstruation begins, hormones stabilize at consistently low levels, ending the withdrawal pattern and fluctuations that drove the mood symptoms 4, 5

Why Progesterone Withdrawal Paradoxically Improves Mood

This seems counterintuitive because progesterone theoretically has anxiolytic and mood-protective properties through its modulation of serotonergic receptors and conversion to allopregnanolone, which acts on GABA-A receptors 2, 6. However:

• The problem is not progesterone itself, but the unstable pattern of rise and fall during the luteal phase 2, 6
• In vulnerable women, insufficient conversion to neuroactive metabolites like allopregnanolone, unstable hormone levels, or decreased receptor sensitivity creates the mood disturbance 6
• When menstruation starts and progesterone remains consistently low (rather than fluctuating), this hormonal stability—even at low levels—is what improves mood 1, 2

The Serotonergic Connection

PMS and PMDD symptoms occur during the luteal phase and disappear within a few days of menstruation onset, which is why SSRIs are first-line therapy for these conditions 4, 7, 8:

• The hormonal fluctuations of the luteal phase appear to interact with serotonergic neurotransmitter systems in vulnerable women 4, 5
• SSRIs reduce overall premenstrual symptoms (SMD -0.57), with continuous administration being more effective than luteal-phase-only dosing 8
• The fact that symptoms resolve at menstruation onset—when hormones stabilize—supports that it is the fluctuation pattern, not hormone presence, causing the problem 4, 5

Individual Vulnerability Determines Who Experiences This Pattern

Not all women experience mood improvement at menstruation because not all women have PMS/PMDD:

• PMS affects 30-40% of reproductive-age women, while PMDD affects only 3-8% 4, 5
• Vulnerability is determined by history of reproductive-related mood disorders, genetic polymorphisms in estrogen receptors and serotonin systems, and differential sensitivity to gonadal steroid changes 1, 2
• Women without this vulnerability do not experience the luteal phase mood disturbance and therefore do not experience relief at menstruation 1, 6

Clinical Pitfalls to Avoid

• Do not assume that supplementing progesterone during the luteal phase will help PMS/PMDD—absolute progesterone levels do not correlate with mood symptoms, and non-bioidentical progestins can actually worsen mood because they cannot be metabolized to mood-improving derivatives like allopregnanolone 2, 6
• Do not attribute the mood improvement to estrogen withdrawal alone—while estrogen fluctuations play a role, the evidence shows it is the overall pattern of hormonal instability (both estrogen and progesterone) that matters 1, 2
• The hallmark diagnostic feature is the predictable, cyclic on/off nature of symptoms that begins in the late luteal phase and remits shortly after menstruation onset 4, 7