PCOS vs. thyroid: what’s the connection?

Polycystic ovary syndrome (PCOS) and thyroid conditions (in particular hypothyroidism) are common, often overlapping, hormonal conditions that can sometimes look similar.

Because their symptoms overlap, it’s not always easy to tell which condition (if any) may be affecting you.

This article explains the similarities and differences between each condition, and how a blood test can help you better understand what’s going on, and your next steps.

We’ll cover:

• How are PCOS and thyroid connected?
• Symptoms PCOS and thyroid conditions have in common
• Differences between PCOS and hypothyroidism
• How to tell the difference between PCOS and thyroid conditions
• Can I have PCOS and hypothyroidism?
• PCOS vs. hypothyroidism: how do they show up in a blood test?
• Does PCOS cause hypothyroidism?

What’s the link between PCOS and thyroid?
 

It’s estimated PCOS (recently renamed polyendocrine metabolic system or PMOS) affects around one in eight to one in ten women in the UK [1,2]. Hyperthyroidism affects around two in 100 people, and is up to ten times more common in women [3–5].

If that’s not enough, research shows PCOS and hypothyroidism commonly coexist [6,7], although the exact relationship isn’t fully understood.

Both PCOS and hypothyroidism affect the endocrine system, meaning they influence hormone balance, but they do so in different ways.

Shared symptoms in PCOS and hypothyroidism
 

Although they affect different hormones, PCOS and hypothyroidism can cause similar symptoms.

The main symptoms that overlap are:

• Fatigue or persistent tiredness
• Weight gain or difficulty losing weight
• Irregular periods

If left unmanaged, both conditions may also be linked to:

• High cholesterol
• Increased cardiovascular risk
• Depression or low mood

These similarities can make it difficult to diagnose PCOS and thyroid conditions without further investigation.

What are the differences between PCOS and hypothyroidism?
 

Although PCOS and thyroid conditions can share outward features, the underlying causes are different.

• PCOS affects your reproductive hormones, which can influence ovulation and androgen levels.
• Hypothyroidism affects your thyroid hormones, which regulate energy levels, metabolism, and body temperature.

This difference is why testing can be helpful – two people with very similar symptoms may have quite different underlying hormone patterns.

Symptoms more specific to PCOS:

• Acne
• Excess facial or body hair (hirsutism)
• Thinning hair on the scalp
• Fertility challenges

Symptoms more associated with hypothyroidism:

• Feeling cold more easily
• Dry skin
• Constipation
• Slower heart rate

How to tell the difference between PCOS and hypothyroidism
 

If you’re not sure what’s causing your symptoms, a blood test or consultation with a doctor is a good place to start.

A blood test can provide useful insight into:

• Which hormones may be out of balance
• Whether one or multiple hormonal systems are involved
• Whether follow-up investigation is needed

While blood tests alone can’t diagnose PCOS, they can help identify patterns that may point towards PCOS, a thyroid dysfunction, or both.

Can I have PCOS and hypothyroidism?
 

Yes, it is possible for PCOS and thyroid conditions to exist together.

Some research suggests that people with PCOS may have a higher likelihood of thyroid disorders, particularly hypothyroidism. When both occur together, symptoms may feel more persistent or complex.

This is why testing a broader hormone profile can be useful.

Does PCOS cause hypothyroidism?

PCOS does not directly cause hypothyroidism.

Whilst a direct connection between the two conditions isn’t clear, the similarities of PCOS and hypothyroidism can cause confusion. Research suggests that if you have PCOS, you may have a higher risk of developing thyroid issues.

PCOS vs. hypothyroidism: how do they show up in a blood test?
 

As PCOS and thyroid conditions can be difficult to tell apart based on symptoms alone, blood testing can help distinguish between the two.

If you have hypothyroidism but not PCOS, blood tests may reflect your altered thyroid hormone production.

You might notice:

• Raised thyroid-stimulating hormone (TSH)
• Lower levels of free thyroxine (T4) and free triiodothyronine (T3)
• Reproductive hormones are within expected ranges

On the other hand, if you have PCOS and don’t have any thyroid condition, blood tests may show:

• Raised androgens (such as testosterone)
• An imbalance in luteinising hormone (LH) and follicle-stimulating hormone (FSH)
• Thyroid hormones are within the reference range

Many blood tests for PCOS include thyroid markers to help rule out thyroid dysfunction.

A more Advanced Thyroid Function Blood Test may show imbalances in your thyroid antibodies too.

PCOS and thyroid FAQs

Can thyroid problems be mistaken for PCOS?

Yes, thyroid problems can be mistaken for PCOS, in the absence of proper testing, because symptoms overlap.

Is weight gain caused by PCOS or hypothyroidism?

Both conditions can contribute to weight changes, but through different hormonal mechanisms.

When should you consider testing?

If you’re experiencing symptoms like fatigue, weight changes, or irregular periods and want clearer answers, testing can be a helpful next step.

References

1. Verity, What is PCOS. In: Verity - The UK PCOS Charity [Internet]. [cited 27 Apr 2026].
2. NHS, Polycystic ovary syndrome. In: nhs.uk [Internet]. 20 Oct 2017 [cited 27 Apr 2026].
3. Thyroid UK, Hypothyroidism - Thyroid UK. 23 Sep 2019 [cited 27 Apr 2026]. 
4. Mendes D, Alves C, Silverio N, Batel Marques F. Prevalence of Undiagnosed Hypothyroidism in Europe: A Systematic Review and Meta-Analysis. Eur Thyroid J. 2019;8: 130–143. doi:10.1159/000499751
5. NICE, Prevalence | Background information | Hypothyroidism | CKS | NICE. [cited 27 Apr 2026]. 
6. Thyroid UK, Polycystic Ovary Syndrome (PCOS) - Thyroid UK. 24 Sep 2019 [cited 27 Apr 2026].
7. Singla R, Gupta Y, Khemani M, Aggarwal S. Thyroid disorders and polycystic ovary syndrome: An emerging relationship. Indian J Endocrinol Metab. 2015;19: 25–29. doi:10.4103/2230-8210.146860