Perimenopause or thyroid problems? How to tell the difference

If you’re feeling constantly fatigued, gaining weight despite no major changes in diet or exercise, struggling with brain fog, or experiencing mood swings, you might assume it’s just perimenopause. But what if your thyroid is involved?

Many of my clients come to me convinced they’re just going through normal hormonal shifts, only to find that their thyroid is playing a significant role in their symptoms. The overlap between perimenopause and thyroid dysfunction - especially hypothyroidism - is significant, making it easy for thyroid issues to go undiagnosed.

So, how can you tell the difference, and what if both are happening at the same time?

Perimenopause vs. hypothyroidism: Understanding the overlap

Both perimenopause and hypothyroidism can cause fatigue, weight gain, brain fog, mood swings, dry skin, hair thinning, and issues with temperature regulation. These similarities mean that many women experiencing thyroid dysfunction are told their symptoms are simply part of the ageing process. While perimenopause does impact metabolism and energy levels, it’s often only part of the picture.

One key factor that links these conditions is estrogen. During perimenopause, estrogen levels fluctuate unpredictably, sometimes spiking higher than normal before eventually declining. What many people don’t realise is that excessive estrogen can suppress thyroid function.

How high estrogen affects thyroid function

Estrogen impacts the thyroid in several ways. First, it increases the production of thyroid-binding globulin (TBG), a protein that binds to thyroid hormones in the bloodstream. When thyroid hormones are bound to TBG, they become inactive, meaning the body can’t use them effectively. This can lead to symptoms of hypothyroidism even if the thyroid is producing adequate amounts of hormone.

Another key issue is the conversion of thyroid hormones. The body primarily produces T4, an inactive form of thyroid hormone that needs to be converted into T3, the active form that directly influences metabolism, energy levels, and brain function. High estrogen levels can interfere with this conversion, leading to low T3 levels - something I frequently see in my clients.

The hidden problem: Normal TSH but low T3

One of the biggest frustrations I see is when clients are told their thyroid function is 'normal' based on a TSH (thyroid-stimulating hormone) test, yet they continue to experience symptoms of hypothyroidism. In many cases, this is because their active thyroid hormone - T3 - is too low, but it hasn’t been tested.

Low T3 can present as persistent fatigue, unexplained weight gain, sluggish digestion, cold hands and feet, depression, and hair thinning. These are symptoms that many assume are part of perimenopause, but in reality, they often indicate a thyroid issue that has been overlooked.

How DUTCH testing can help

One of the best tools for assessing the connection between perimenopause and thyroid health is the DUTCH test (Dried Urine Test for Comprehensive Hormones). Unlike standard blood tests, which provide a snapshot of hormone levels at a single moment in time, the DUTCH test measures hormone fluctuations throughout the day and assesses how estrogen, progesterone, cortisol, and other key hormones are being metabolised.

For those in perimenopause with suspected thyroid issues, this test can reveal whether estrogen dominance is contributing to suppressed thyroid function. It also provides insight into how well the liver is metabolising estrogen, which is crucial because poor estrogen clearance can keep levels high and continue to interfere with thyroid hormone conversion.

Another advantage of the DUTCH test is its ability to measure adrenal function. Chronic stress, which is common in perimenopause, can elevate cortisol levels, further inhibiting T4-to-T3 conversion and worsening symptoms of hypothyroidism.

Many women I work with who are experiencing low energy, brain fog, and weight gain, are dealing with a combination of thyroid dysfunction, high estrogen, and dysregulated cortisol. The DUTCH test helps identify where the biggest imbalances are so that a targeted plan can be created.

What you can do to support your thyroid and hormonal balance

If you suspect that both perimenopause and thyroid dysfunction are contributing to your symptoms, the first step is to get proper testing. A full thyroid panel - including Free T3, Free T4, Reverse T3, and thyroid antibodies - can provide a clearer picture than just TSH alone. Pairing this with DUTCH testing allows you to see how estrogen and cortisol may be influencing thyroid function.

Once you have a clearer understanding of your hormone levels, targeted interventions can make a significant difference. Supporting liver health is crucial because the liver is responsible for metabolising estrogen and converting T4 to T3. Nutrients like selenium, zinc, and iodine (in the right amounts) are also essential for thyroid function and can help improve T3 levels. Reducing stress and balancing blood sugar are equally important, as chronic stress and high insulin levels can suppress thyroid activity.

For women with high estrogen, dietary changes can help promote better hormone balance. Increasing cruciferous vegetables (such as broccoli, cauliflower, and kale) supports estrogen detoxification, while reducing alcohol and processed foods helps the liver function optimally. For some women, addressing progesterone levels is also important, as progesterone naturally declines in perimenopause and plays a role in balancing estrogen.

If you’re struggling with exhaustion, unexplained weight gain, brain fog, or mood swings and have been told it’s just part of getting older, it’s worth looking deeper. Perimenopause and thyroid dysfunction often occur together, and high estrogen can directly impact thyroid function, particularly by lowering active T3 levels.

DUTCH testing offers valuable insights into hormone metabolism, helping to identify whether estrogen dominance or adrenal dysfunction is contributing to thyroid symptoms. When thyroid dysfunction is properly addressed - rather than dismissed as a normal part of perimenopause - many of my clients find they regain their energy, mental clarity, and ability to maintain a healthy weight.

If this resonates with you, consider working with a practitioner like me who understands the connection between thyroid and perimenopausal health. You don’t have to accept exhaustion and metabolic slowdowns as inevitable - there are steps you can take to feel like yourself again.