Your thyroid and your cycle

Your thyroid makes hormones that set the pace for loads of body systems, including your menstrual cycle. When it runs too slow or too fast, your periods often notice.

Underactive vs overactive

• Underactive (hypothyroidism): tiredness, feeling cold, weight gain, dry skin and hair, low mood, and irregular or heavy periods
• Overactive (hyperthyroidism): racing heart, trouble sleeping, weight loss, feeling hot and sweaty, anxiety or irritability, and sometimes lighter, less frequent or missing periods

Both can affect fertility, and many symptoms overlap with stress, PMS or anaemia, which is why a simple blood test is so useful.

Getting checked

A GP can arrange a thyroid function blood test, which usually starts with TSH. Both conditions are very treatable, usually with daily tablets (for underactive) or medicines that calm thyroid activity (for overactive). NICE heavy-bleeding guidance says thyroid tests are not needed for heavy periods alone unless there are other signs of thyroid disease, so mention any other symptoms.

If you have an underactive thyroid and are pregnant or planning a pregnancy, tell your GP early. Your dose of levothyroxine will probably need to change, and untreated thyroid problems can raise the chance of complications.