Thyroid and Your Periods: How Thyroid Problems Affect Your Cycle

The short answer: Your thyroid makes hormones that set the pace of almost everything in your body, including your menstrual cycle. An underactive thyroid (hypothyroidism) tends to make periods heavier, longer or irregular. An overactive thyroid (hyperthyroidism) tends to make them lighter, less frequent or stop altogether. A simple blood test checks your thyroid, and once it's treated, periods usually settle. If your cycle has changed and you also feel unusually tired, cold, hot, anxious or are gaining or losing weight, see a doctor.

What your thyroid does

Your thyroid is a small, butterfly-shaped gland at the front of your neck, just below your voice box. It makes two main hormones: thyroxine (T4) and triiodothyronine (T3). Together they control your metabolism, which simply means how fast your body uses energy.

Thyroid hormones affect your heart rate, body temperature, digestion, mood, skin, hair and weight. They also talk to the hormones that run your menstrual cycle. When thyroid levels are too low or too high, the signals between your brain and your ovaries can get muddled, and ovulation (the release of an egg) may become irregular.

The thyroid is controlled by the pituitary gland in your brain. The pituitary makes thyroid-stimulating hormone (TSH), which tells the thyroid how much hormone to produce. This is why TSH is usually the first thing a doctor checks. If you'd like to understand the cycle hormones themselves, our guide to the hormones behind your menstrual cycle explains them phase by phase.

How common are thyroid problems in Indian women?

A study across eight Indian cities, published in the Indian Journal of Endocrinology and Metabolism in 2013, tested more than 5,000 adults and found that about 1 in 10 had hypothyroidism (10.95%). Women and older adults were more likely to be affected.

The same study found that around a third of the people with hypothyroidism had no idea they had it: 3.47% of everyone tested was newly picked up, compared with 7.48% who already knew.

So if you're tired all the time and your periods have changed, a thyroid problem is worth ruling out. An overactive thyroid is less common, but the NHS notes it is about ten times more common in women than men and usually starts between the ages of 20 and 40.

Underactive thyroid (hypothyroidism) and your periods

With an underactive thyroid, your body doesn't make enough thyroid hormone, so many processes slow down. The most common cause is Hashimoto's disease, an autoimmune condition where your immune system attacks the thyroid. It's most common in women and often starts between 30 and 50, but it can begin at any age, including in teenagers.

Period changes you may notice

• Heavier periods: soaking through pads or period panties faster than you used to, or passing more clots.
• Longer periods: bleeding for more days than your usual pattern.
• Irregular cycles: periods arriving earlier or later than expected.
• Missed periods: in some women, periods can stop for a few months.

The NHS lists irregular or heavy periods among the symptoms of an underactive thyroid. Heavy bleeding month after month can lower your iron levels and leave you anaemic, which adds to the tiredness. If you're not sure whether your flow counts as heavy, our guide on how much bleeding is too much has practical ways to judge.

Other symptoms of an underactive thyroid

• Feeling extremely tired, even after a full night's sleep
• Feeling cold when others are comfortable
• Putting on weight without changing how you eat
• Constipation
• Difficulty concentrating, or feeling foggy
• Low mood or depression
• Dry skin, dry hair or hair loss
• A croaky or hoarse voice

These symptoms creep in slowly, so many women put them down to work, children or age. Hair thinning is a common complaint, and our guide to hair fall, facial hair and your hormones covers the other causes too.

Overactive thyroid (hyperthyroidism) and your periods

With an overactive thyroid, your body makes too much thyroid hormone, so things speed up. The most common cause is Graves' disease, another autoimmune condition. Lumps in the thyroid (nodules) that make extra hormone, and some medicines, can also cause it.

Period changes you may notice

• Lighter periods: less blood than usual, or a shorter bleed.
• Fewer periods: longer gaps between them.
• Periods stopping: sometimes for several months, which doctors call amenorrhoea.

The US Office on Women's Health describes hyperthyroidism as causing fewer and lighter periods than usual. If your bleed has suddenly become scanty, our guide on why your period might be suddenly lighter covers other reasons as well.

Other symptoms of an overactive thyroid

• Nervousness, anxiety, irritability or mood swings
• Difficulty sleeping, yet feeling tired all the time
• Feeling hot and sweating more than others
• A fast or irregular heartbeat (palpitations)
• Losing weight even though you're eating more
• A swelling in the neck (goitre)

Underactive vs overactive thyroid at a glance

Not everyone has every symptom, and some, like tiredness and hair loss, can happen with both.

Thyroid problems are one of several causes of an unpredictable cycle. If your thyroid test comes back normal, our guide to irregular periods explains the other common reasons, from stress to PCOS.

Thyroid tests and what the results mean

Checking your thyroid is quick: one blood sample from your arm. Thyroid tests are widely available at diagnostic labs and government hospitals across India. Your doctor or lab will tell you if any other tests ordered alongside need a fasting sample.

The main tests

• TSH (thyroid-stimulating hormone): the signal from your brain. It works like a thermostat. When your thyroid is slow, the brain shouts louder, so TSH goes up. When your thyroid is overactive, the brain goes quiet, so TSH goes down.
• T4 (thyroxine), often reported as free T4 or FT4: the main hormone your thyroid makes.
• T3 (triiodothyronine), or FT3: sometimes checked, especially if an overactive thyroid is suspected.
• Thyroid antibodies: sometimes tested to see whether an autoimmune condition like Hashimoto's or Graves' disease is the cause.

Reading the results in plain words

• High TSH with low T4: usually means an underactive thyroid.
• Low TSH with high T4 and/or T3: usually means an overactive thyroid. The NHS describes this pattern for hyperthyroidism.
• Slightly high TSH with normal T4: doctors call this subclinical hypothyroidism, a mild form. Your doctor may repeat the test after a few weeks, or treat it if you have symptoms, are trying for a baby or are pregnant.

Normal ranges differ between labs and change with age and pregnancy, so take your report to your doctor, along with a note of your period dates for the last three months.

Thyroid, fertility, pregnancy and after birth

Because thyroid problems can disturb ovulation, they can make it harder to get pregnant. Untreated thyroid disease in pregnancy also raises the risk of problems such as pre-eclampsia (high blood pressure in pregnancy), miscarriage and premature birth. The good news is that treatment usually brings these risks down.

• If you're trying for a baby and have irregular periods, ask your doctor whether a thyroid test makes sense.
• If you already take thyroid medicine, tell your doctor as soon as you plan a pregnancy or find out you're pregnant. Your dose often needs adjusting, and you'll have more frequent blood tests.
• If you take medicine for an overactive thyroid, ask about contraception and pregnancy planning, as some treatments need to be changed before or during pregnancy.

If you're pregnant and have had thyroid problems before, or have symptoms, it's fine to ask your doctor whether you need a thyroid test.

Postpartum thyroiditis: thyroid changes after birth

Some women develop inflammation of the thyroid in the first year after having a baby. This is called postpartum thyroiditis. It often starts with a short overactive phase (feeling jittery, hot, losing weight fast, poor sleep even when the baby sleeps), followed by an underactive phase (exhaustion, low mood, weight gain, feeling cold).

These symptoms are easily blamed on sleepless nights, so it often goes unnoticed. For many women it settles on its own, but some are left with a long-term underactive thyroid that needs treatment.

If your periods return very heavy, or don't return long after you've stopped breastfeeding, mention it to your doctor. Our guide to your first period after pregnancy explains what's usual.

How thyroid problems are treated

Treatment depends on the type of problem and its cause. Most women go on to live normal lives once hormone levels are back in range.

Underactive thyroid

Your doctor will usually prescribe levothyroxine, a tablet that replaces the missing hormone. It's taken daily, often for life. You'll need regular blood tests at first to find the right dose, then less often once you're stable. Tell your doctor or pharmacist if you feel unwell after a dose change.

Overactive thyroid

Your doctor may suggest anti-thyroid medicine to reduce hormone production, radioiodine treatment to shrink overactive thyroid tissue, or surgery to remove part or all of the gland. An endocrinologist (a hormone specialist) usually helps you decide.

How long until periods settle?

It can take a few months for your cycle to settle after treatment starts, so keep tracking. If your periods are still heavy or irregular once your thyroid levels are normal, ask your doctor to look for other causes.

Living with a thyroid condition day to day

• Take your tablet the same way every day: follow your doctor's or pharmacist's advice about timing, food and other medicines, as some supplements, such as iron and calcium, can affect how thyroid tablets are absorbed.
• Keep your follow-up tests: doses often need small changes, especially after pregnancy, big weight changes or new medicines.
• Use iodised salt in normal amounts: iodine is needed to make thyroid hormone, and iodised salt is the main source for most Indian families. Don't take iodine or kelp supplements unless your doctor advises it.
• Look after your iron: if your periods are heavy, include iron-rich foods such as palak, rajma, chana, jaggery and dates, with amla or lemon to help absorption, and ask whether you need a haemoglobin test.
• Be wary of "thyroid cure" products: no herbal powder, special diet or detox replaces proper treatment.

Staying comfortable while your cycle settles

Heavy, long or unpredictable periods are hard to plan around. If your flow is heavy, a period panty can be worn on its own or as a backup to a pad. It has one absorbency for every flow and can be worn for up to 8 hours depending on how heavy you are. High waist styles give more front-to-back coverage at night.

If your periods have become light or patchy with an overactive thyroid, panty liners are often all you need on spotting days, and they're handy to keep in your bag when you can't predict when bleeding will start.

When to see a doctor or get urgent help

See a doctor if

• Your periods have become heavier, longer, lighter or irregular and you don't know why
• You've missed three periods in a row and you're not pregnant
• You have symptoms of an underactive or overactive thyroid, such as constant tiredness, feeling too cold or too hot, or unexplained weight change
• You notice a swelling or lump in your neck
• You're trying to get pregnant and your cycle is irregular
• You're pregnant or planning a pregnancy and take thyroid medicine

Get urgent help if

Call 112 or 108, or go to the nearest hospital emergency department, if you have:

• A very fast heartbeat with a high temperature, severe agitation or confusion, or yellowing of the skin or eyes. These can be signs of a thyroid storm, a rare but life-threatening flare-up of an overactive thyroid.
• Very heavy bleeding, soaking through a pad or period panty every hour for a few hours, or feeling faint or dizzy

Frequently asked questions

Can thyroid problems cause irregular periods? Yes. Both an underactive and an overactive thyroid can disturb ovulation, so periods may come early, late or not at all. A TSH blood test is one of the first checks doctors do for irregular periods.

Does hypothyroidism cause heavy periods? It often does. Heavier and longer periods are typical of an underactive thyroid, although some women have irregular or missed periods instead.

Can hyperthyroidism stop your periods? It can. An overactive thyroid tends to make periods lighter and less frequent, and in some women they stop for months until the thyroid is treated.

Will my periods become regular after thyroid treatment? For most women, yes, once hormone levels are back in the normal range. It can take a few months, so keep tracking and tell your doctor if things don't improve.

What is a normal TSH level? It depends on the lab, your age and whether you're pregnant, so check the range printed on your report and ask your doctor to explain it. A high TSH usually points to an underactive thyroid and a low TSH to an overactive one.

Can I get pregnant with a thyroid problem? Yes, many women do. Getting your thyroid well controlled before and during pregnancy improves your chances and lowers risks, so speak to your doctor early.

Is thyroid linked to PCOS? They're separate conditions, but both can cause irregular periods, weight changes and hair problems, and some women have both. Your doctor may test for both. Our guide to the long-term health risks of PCOS covers the checks recommended for PCOS.

Related reading

• Irregular Periods: Causes, Tests and What Helps
• The Hormones Behind Your Menstrual Cycle, Phase by Phase
• Hair Fall, Facial Hair and Your Hormones: What's Normal and What Helps
• Period Late but Not Pregnant? 10 Common Reasons

This article is for general information and doesn't replace advice from your doctor.

Sources: NHS: Underactive thyroid (hypothyroidism), NHS: Overactive thyroid (hyperthyroidism), diagnosis, NHS: Overactive thyroid (hyperthyroidism), complications, Office on Women's Health: Thyroid disease fact sheet, Unnikrishnan AG et al. Indian Journal of Endocrinology and Metabolism: Prevalence of hypothyroidism in adults: An epidemiological study in eight cities of India (2013)