When a period stops

What it is

Not having periods is called amenorrhea. A late or missed period can happen for many reasons, and most of the time it's nothing to worry about.¹ But periods are a sign of how the body is doing overall, so when they stop for months, it's worth finding out why.

First, rule out pregnancy. It's the most common reason a period stops, and a home pregnancy test is the place to start.¹

Common causes

The NHS lists these:¹

pregnancy
stress
sudden weight loss
being overweight
doing too much exercise
some hormonal birth control: the combined pill, the shot and the hormonal IUD
breastfeeding
PMOS (formerly PCOS)
an overactive or underactive thyroid, and other conditions such as diabetes
, usually between 45 and 55
normal variation: some people's cycles just vary

When the brain hits pause

The cycle starts in the brain. The hypothalamus sends the first hormone signal that sets off each cycle. When it senses that the body is under too much stress, or isn't getting enough energy, it can slow or stop that signal, and periods stop. This is called hypothalamic amenorrhea.²

Its common causes are eating too little, exercising a lot, and emotional stress, and they often come together.² It's often linked with athletes, but it's also common in teenagers and in anyone under stress at work or home.² Besides missing periods, people may notice mood changes, poor sleep, low energy and hair loss.²

It matters because the hormones that run the cycle also protect the body. Without them, bones can weaken over time, which can lead to osteoporosis, and the risk of heart disease and of trouble getting pregnant goes up.² Periods usually come back once the cause is addressed, often after three to six months of eating enough for the body's activity, easing off intense exercise and managing stress.²

Myth: Losing your period from training means you're fit.

In many sports this has long been seen as a sign of hard training, so it's easy to believe. A period that stops from heavy training and too little food is a sign the body is short on energy, and it can cost bone strength.² It's a reason to talk to a doctor, not a goal.

When to see a doctor

See a doctor if:^1,3,4

you've missed three periods in a row
your periods haven't started by 15
you've missed a period and also notice weight gain or loss, tiredness, new facial hair, or dry or oily skin
your periods have become irregular
for teens: there are 90 days between periods, even once

Recap

Missing a period is common, and pregnancy is the first thing to rule out.
Stress, sudden weight loss, eating too little, too much exercise, PMOS, thyroid problems, breastfeeding, some birth control and perimenopause can all stop periods.
When the brain senses too much stress or too little energy, it can turn down the signals that run the cycle. That can weaken bones over time.
See a doctor after three missed periods in a row, or no period by 15.

Words to know 4

amenorrhea	The medical word for not having periods.
hypothalamic amenorrhea	When periods stop because the brain's hypothalamus slows the hormone signals that run the cycle, often from stress, undereating or heavy exercise.
hypothalamus	A region at the base of the brain that sends the first hormone signal of the cycle.
perimenopause	The years before menopause, when periods become irregular.