Is it perimenopause or your thyroid?

By Shweta Arora, MD, board-certified physician · Medically reviewed by Robin Arora, MD · Updated October 2026

You finally mention the exhaustion, the brain fog and the five pounds that won’t budge, and you hear “it’s probably perimenopause.” Sometimes it is. Sometimes it’s your thyroid. Quite often, it’s both.

Two changes, same decade

Thyroid problems are common in women. According to the American Thyroid Association, women are five to eight times more likely than men to have thyroid problems, about one woman in eight will develop one in her lifetime, and up to 60% of people with thyroid disease don’t know it.

Midlife is a common time for both changes to show up. In the SWAN study of more than 3,000 U.S. women aged 42 to 52, about 1 in 10 already had a thyroid-stimulating hormone (TSH) level outside the normal range.

The symptom overlap

Perimenopause and an underactive thyroid (hypothyroidism) can both cause:

• Fatigue and low energy
• Weight gain or trouble losing weight
• Brain fog and trouble concentrating
• Low mood or anxiety
• Poor sleep
• Low libido
• Changes in your periods

An overactive thyroid can mimic perimenopause too: feeling hot, sweating, a racing heart, anxiety and trouble sleeping.

Clues that point one way or the other

• Timing. Symptoms that rise and fall with your cycle (worse sleep, irritability or anxiety the week before your period) point toward hormone swings. Symptoms that stay the same all month are worth a thyroid check.
• Hot flashes, night sweats and vaginal dryness usually come from falling estrogen, not from an underactive thyroid.
• Feeling cold, constipation, dry skin and thinning hair are classic underactive-thyroid signs.
• What changed this year. In one study, people who had many symptoms that were new or worse over the past year were much more likely to have an underactive thyroid than people whose symptoms had been stable. Keep a list.

“My labs are normal, but I don’t feel normal”

A thyroid check usually starts with TSH. Depending on your symptoms and history, it may make sense to add:

• Free T4, the main hormone the thyroid makes.
• Thyroid antibodies (TPO). They point to autoimmune thyroid disease, the most common cause of an underactive thyroid. In a 20-year study of women, those with both a raised TSH and positive antibodies were far more likely to develop an underactive thyroid over time.

“Subclinical” hypothyroidism means TSH is a little high while free T4 is still normal. It affects up to 10% of adults. Whether to treat it depends on how high the TSH is, your symptoms, your age, your antibodies and whether you’re planning pregnancy. It’s a conversation, not an automatic yes or no.

Get labs drawn the same way each time, with the same lab and at about the same time of day, so results can be compared fairly. TSH naturally runs higher in the morning than in the afternoon.

Already on thyroid medication and still not right?

You’re not alone. In a Mayo Clinic chart review, about 1 in 4 people on thyroid medication still had symptoms even though their TSH was normal. An older study of more than 25,000 people found that about 40% of those taking thyroid medication had a TSH outside the normal range.

Worth reviewing with your clinician: how and when you take your dose, other medicines that affect absorption, iron and vitamin levels, sleep, mood, and whether perimenopause is adding its own symptoms on top.

Starting or stopping estrogen? Check your thyroid too

Estrogen taken by mouth raises a blood protein that carries thyroid hormone, which can lower the amount of free hormone available. In a study in the New England Journal of Medicine, 7 of 18 women on thyroid medication needed a higher dose after starting estrogen by mouth. Estrogen through the skin has much less effect on that protein.

If you take thyroid medication, ask whether to recheck your thyroid levels in the weeks after starting, stopping or changing estrogen.

How we look at the whole picture

At a hormone visit we review your cycle, symptoms and history, check your thyroid when it’s indicated, and coordinate with your primary care clinician or endocrinologist when needed. Every plan is individualized, and treatment is recommended only when it’s right for you.

Every plan is individualized, and treatment is recommended only when it’s right for you after your consultation.

Related reading: Perimenopause: symptoms, diagnosis and treatment · Do I need my hormones tested? · Mood, sleep & brain fog in midlife. Browse the full Women’s Health Library.

See us in person or by video

Visit our physician-led team at our Hudson, Ohio or Barboursville, West Virginia office, or meet Dr. Robin Arora by telehealth from anywhere in Ohio, West Virginia, Kentucky or Florida.

Sources: American Thyroid Association press room (general thyroid statistics); Sowers et al., Clinical Endocrinology 2003 (SWAN); Canaris et al., J Gen Intern Med 1997 and Arch Intern Med 2000; Vanderpump et al., Clinical Endocrinology 1995 (Whickham survey); Biondi, Cappola & Cooper, JAMA 2019; Hidalgo et al., Endocrine Practice 2024 (via American Thyroid Association); Arafah, NEJM 2001. This page is general education, not medical advice.