If you have PCOS and you're exhausted, gaining weight you can't explain, and still getting fobbed off with "it's just PCOS", it might not be just PCOS. Hypothyroidism (an underactive thyroid) shares a striking number of symptoms with PCOS, and research suggests it turns up more often in women with PCOS than in the general population. The two conditions are diagnosed with different blood tests and treated in completely different ways, so telling them apart matters. This guide breaks down what hypothyroidism actually is, how it overlaps with PCOS, and exactly what to ask your GP for so you're not stuck guessing which condition is driving your symptoms.

What Is Hypothyroidism, Exactly?

Hypothyroidism is an underactive thyroid gland that doesn't produce enough thyroid hormone, slowing down your metabolism, energy, mood and periods.

Your thyroid is a small, butterfly-shaped gland at the base of your neck. It makes hormones (T3 and T4) that control the speed of pretty much every system in your body: metabolism, heart rate, temperature, digestion, and yes, your menstrual cycle too. When it's underactive, everything runs slower than it should.

In the UK, the most common cause is an autoimmune condition called Hashimoto's thyroiditis, where your immune system mistakenly attacks the thyroid gland itself. It mostly affects women, and it usually shows up between the ages of 30 and 50, although it can happen at any age.^[1]

According to NICE guidance, hypothyroidism affects around 2% of the UK population, rising to more than 5% of people over 60, and women are 5 to 10 times more likely to develop it than men.^[2] That's not a rare condition. It's a common one that gets missed constantly, partly because the symptoms are so easy to write off as "just being busy" or "just getting older."

Left untreated, hypothyroidism is usually a straightforward, well-managed condition once diagnosed. It's treated with daily levothyroxine tablets, which replace the hormone your thyroid isn't making enough of. It is not something a supplement, diet change or "holistic reset" can substitute for. This is a medical condition that needs a medical diagnosis and, in most cases, lifelong medication and monitoring.

How Are PCOS and Hypothyroidism Connected?

PCOS and hypothyroidism aren't the same condition, but they share hormonal pathways, so having one appears to raise the odds of developing the other.

You're not imagining it if you've noticed your PCOS symptoms and "possible thyroid stuff" seem to overlap. They're not the same condition, and one doesn't cause the other in a simple, direct line. But researchers have found real biological links between them.

One proposed mechanism involves insulin resistance, which is central to PCOS for most women. Insulin resistance and higher body fat can affect how your body converts and uses thyroid hormone, and can push TSH (thyroid stimulating hormone) upward even before T4 levels change. There's also a hormonal angle: PCOS is associated with higher oestrogen exposure relative to progesterone, and researchers think this may encourage the kind of immune activity that contributes to autoimmune thyroid conditions like Hashimoto's.^[3]

None of this means PCOS "causes" hypothyroidism, or the other way round. It means the two conditions share enough biological territory that having one is a reason to get properly checked for the other, not a reason to assume every new symptom is "just" the condition you already have.

This is exactly the kind of overlap that leads to years of misdiagnosis. If your GP diagnosed PCOS and stopped there, and your fatigue, weight changes or hair thinning have gotten worse rather than better, it's worth asking whether your thyroid has ever actually been tested. Not assumed. Tested.

How Common Is Hypothyroidism Alongside PCOS?

Subclinical hypothyroidism appears roughly 2 to 3 times more often in women with PCOS than in women without it, based on published research.

The numbers here are worth knowing, because they explain why this overlap gets talked about so much in PCOS communities.

One frequently cited study found subclinical hypothyroidism (a milder, earlier-stage form where TSH is raised but T4 is still normal) in 22.5% of women with PCOS, compared with 8.75% of women without PCOS.^[3] A separate study in younger women with PCOS put the figure at 11.3%.^[3] For context, subclinical thyroid dysfunction is estimated to affect around 4 to 6% of women of reproductive age generally.^[3]

Thyroid autoimmunity (the antibodies that flag conditions like Hashimoto's) also shows up more often in PCOS: one study found thyroid peroxidase (TPO) antibodies in 27% of women with PCOS, compared with 8% of controls.^[3]

These are associations, not guarantees. Having PCOS doesn't mean you will develop a thyroid condition. It means the odds are higher than for the general population, which is exactly why routine thyroid screening is worth asking for if you haven't had it done, especially if you were diagnosed with PCOS some time ago and never had a full thyroid panel alongside it.

What Symptoms Overlap Between PCOS and Hypothyroidism (and How Do You Tell Them Apart)?

Fatigue, weight changes, hair thinning and irregular periods show up in both conditions, which is exactly why so many women end up misdiagnosed or only partly diagnosed.

This is the part that trips almost everyone up. PCOS and hypothyroidism can look almost identical from the inside. You're tired all the time. Your weight is doing things that don't match your diet or exercise. Your hair is coming out in the shower. Your periods are unpredictable. Which condition is actually behind it? Sometimes it's one. Sometimes it's both. You genuinely cannot tell from symptoms alone, and neither can your GP without blood tests.

Symptom	More typical of PCOS	More typical of hypothyroidism	Can overlap in both
Irregular or missed periods	Common, often with long cycles	Can occur, often heavier or more spaced out	Yes
Weight gain / difficulty losing weight	Common, linked to insulin resistance	Common, linked to slowed metabolism	Yes
Fatigue	Common	Common, often described as bone-deep	Yes
Hair thinning	Scalp thinning with facial/body hair growth	Diffuse thinning, sometimes eyebrow loss (outer third)	Yes
Acne	Common, jawline/chin pattern	Less typical	Rare
Excess facial/body hair (hirsutism)	Common, linked to higher androgens	Not typical	No
Cold intolerance	Not typical	Common	No
Dry skin, brittle nails	Occasional	Common	Yes
Low mood / brain fog	Common	Common	Yes

Notice the pattern: acne and hirsutism (excess facial or body hair) point more towards PCOS and its higher androgen levels, while cold intolerance points more towards an underactive thyroid. Everything else in the middle column can genuinely go either way, or both. That "either way" column is exactly why blood tests, not symptom-spotting, are what actually settles this. If your fatigue, hair loss or weight changes are getting worse rather than better with the treatment you're already on, that's worth flagging, not brushing off. For more on how PCOS symptoms typically present, see our guide to the first signs of PCOS and our deeper look at PCOS fatigue.

How Is Hypothyroidism Diagnosed, and How Is That Different From PCOS Testing?

Hypothyroidism is diagnosed with a TSH and free T4 blood test, which is a different panel from the hormone tests used to diagnose PCOS.

Here's where a lot of confusion happens: PCOS and hypothyroidism are picked up using different blood tests, and having one panel done doesn't mean the other has been checked.

To diagnose hypothyroidism, a GP will usually order:

• TSH (thyroid stimulating hormone): the first-line test. A raised TSH is usually the earliest sign something's off.
• Free T4 (thyroxine): checked alongside TSH to confirm whether the thyroid itself is underactive.
• Thyroid antibodies (TPO antibodies): sometimes tested to check for autoimmune thyroid disease such as Hashimoto's, particularly if TSH is borderline or there's a family history.

PCOS, by contrast, is typically assessed with a different set of markers: androgens (like testosterone), LH and FSH, and often a pelvic ultrasound alongside your symptom history. The research on this is actually pretty clear that these are two distinct diagnostic pathways, which is exactly why a PCOS diagnosis alone tells you nothing about your thyroid status, and a normal thyroid result tells you nothing about your PCOS. Each needs its own testing. We've written a full breakdown of which blood tests to ask for with PCOS if you want the complete list, and a separate guide on how doctors diagnose PCOS in the first place.

If you've only ever had one set of tests done, whichever it was, that's a gap worth closing.

What Should You Ask Your GP For?

Ask specifically for a TSH and free T4 test, and mention any symptoms (fatigue, cold intolerance, hair thinning, weight change) that haven't improved with your current PCOS management.

Your diagnosis is a starting point, not a verdict. If you have PCOS and your symptoms don't add up, or they're not responding the way you'd expect, it's completely reasonable to go back and ask for more.

Specifically, it helps to say:

• "Can I have a thyroid function test, specifically TSH and free T4?" Naming the tests avoids a vague "we'll keep an eye on it" response.
• "I have PCOS and I'm having [symptom], which hasn't improved. Could this be thyroid-related?" This links your symptoms to a specific, testable hypothesis rather than a general complaint.
• "Is there a family history of thyroid disease I should mention?" If a parent, sibling or grandparent has Hashimoto's or any thyroid condition, say so. It raises your risk and it's relevant.
• "Should I also be tested for thyroid antibodies (TPO)?" Worth asking if your TSH comes back borderline rather than clearly high or clearly normal.

If you're told your thyroid is "fine" based on a TSH result you've never actually seen the number for, ask for the figure and the reference range. You're entitled to that information, and it's genuinely useful to track over time, especially if symptoms persist.

Already diagnosed with hypothyroidism and taking levothyroxine? Keep taking it as prescribed, keep your monitoring appointments, and speak to your GP or pharmacist before adding any new supplement, including ones aimed at general hormone or cycle support. Some supplements and minerals can interfere with how levothyroxine is absorbed if taken too close together, so timing matters even when a product has nothing to do with thyroid function itself.

What Can You Do Alongside Medical Treatment?

Thyroid treatment has to come from your GP, but general lifestyle habits and cycle-support basics can still be part of looking after your wider hormonal health.

To be direct: nothing in this section treats, manages or improves thyroid function. Hypothyroidism needs proper medical diagnosis and, in most cases, levothyroxine. That's not negotiable, and no supplement replaces it.

What you can do, alongside whatever your GP has prescribed, is pay attention to the basics that support your body more broadly: regular movement, protein and fibre at meals to support blood sugar balance, decent sleep, and stress that's managed rather than ignored. None of this is groundbreaking, and none of it is a substitute for medication if you need it. It's simply what gives your body a fair shot at feeling steadier while your thyroid treatment does its job.

If your main frustration is with your broader menstrual cycle and PCOS symptoms rather than anything thyroid-related, that's where general hormonal support supplements can have a role, as one part of a wider approach alongside proper diagnosis and, where needed, medical treatment. Myoplus is formulated with myo-inositol for general hormonal and menstrual cycle support. It isn't designed for, marketed for, or intended to affect thyroid function, thyroid hormone levels, or hypothyroidism in any way, and it should not be treated as one. If you're on levothyroxine or have a diagnosed thyroid condition, speak to your GP or pharmacist before adding it, just as you would with any new supplement.

Frequently Asked Questions

Can PCOS cause hypothyroidism?
No, PCOS doesn't directly cause hypothyroidism. The two conditions share overlapping hormonal and metabolic pathways, including insulin resistance, which may explain why hypothyroidism and thyroid antibodies show up more often in women with PCOS than in the general population.^[3]

Can hypothyroidism be mistaken for PCOS, or the other way round?
Yes, easily. Fatigue, weight gain, irregular periods and hair thinning appear in both conditions, and without blood tests for both, it's genuinely difficult to tell them apart on symptoms alone.

What blood tests show hypothyroidism specifically?
TSH (thyroid stimulating hormone) and free T4 are the standard first-line tests. TPO antibodies may also be checked if autoimmune thyroid disease is suspected.

Should everyone with PCOS get their thyroid checked?
Guidelines don't currently recommend universal thyroid screening for every woman with PCOS, but given how often the two overlap, it's a reasonable and low-risk test to request, especially if you have symptoms that haven't resolved.

Will treating my thyroid improve my PCOS symptoms?
If you have both conditions, treating hypothyroidism with levothyroxine may ease symptoms that overlap between the two, like fatigue or irregular periods, but it won't resolve PCOS-specific features like elevated androgens. They're managed separately.

Can supplements treat an underactive thyroid?
No. Hypothyroidism requires medical diagnosis and, in most cases, levothyroxine prescribed and monitored by a GP or endocrinologist. No supplement, including anything from MyOva, is designed or intended to treat, manage or affect thyroid function.

Conclusion

PCOS and hypothyroidism are two separate conditions that happen to speak a similar symptom language: fatigue, weight changes, hair thinning, irregular periods. That overlap is exactly why so many women end up with one diagnosis and a long list of symptoms nobody's fully explained. Your body is trying to tell you something, and "it's probably just your PCOS" isn't always the full answer.

Hormonal literacy isn't complicated, it's just rarely taught. Knowing that these two conditions need different blood tests, and that a diagnosis of one doesn't rule out the other, puts you in a stronger position to ask your GP the right questions. If your symptoms have plateaued, worsened, or never quite matched your PCOS diagnosis, a TSH and free T4 test is a reasonable, specific, evidence-based thing to ask for. This is what we wish someone had told us sooner, and it's why we keep writing about it.

Further reading

• What blood tests should I ask for with PCOS? The complete guide
• How your doctor might diagnose PCOS
• Understanding and managing PCOS fatigue
• PCOS hair loss: what you can do about it
• PCOS and irregular periods

References

1. NHS. "Underactive thyroid (hypothyroidism)." nhs.uk. Reviewed 2023. https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/
2. National Institute for Health and Care Excellence (NICE). "Thyroid disease: assessment and management, Context." NICE guideline NG145. https://www.nice.org.uk/guidance/ng145/chapter/Context
3. Singla R, Gupta Y, Khemani M, Aggarwal S. "Thyroid disorders and polycystic ovary syndrome: An emerging relationship." Indian Journal of Endocrinology and Metabolism. 2015 Jan-Feb;19(1):25-29. https://pmc.ncbi.nlm.nih.gov/articles/PMC4287775

References