When your cycle stops: FHA vs PCOS

If your periods have become irregular, very light, or stopped altogether, there are two common explanations that require opposite responses — and they are frequently confused.

Functional hypothalamic amenorrhea (FHA) is chronic anovulation driven by energy deficit, psychological stress, excessive exercise, or a combination. Stress signalling suppresses the pulsing GnRH signal that drives the whole cycle. It is a diagnosis of exclusion, and the Endocrine Society's clinical practice guideline is unambiguous about first-line treatment: correct the energy imbalance — more intake, better nutrition, less training — with medical, dietary and mental-health support (Gordon, JCEM 2017). An energy availability target of roughly 30 kcal per kg of fat-free mass per day is used to prevent and reverse it.

Why the confusion is harmful. FHA is often misread as PCOS. The standard PCOS advice — eat less, exercise more — is precisely the wrong prescription for someone already in energy deficit, and it deepens the problem.

This matters beyond fertility: bone density loss and neuropsychiatric effects accumulate while cycles are absent, so it is worth recognizing early even if you are not currently trying to conceive.