A slow thyroid, also called hypothyroidism, arises when your thyroid makes too little hormone. Common complaints are fatigue, feeling cold and weight gain. The diagnosis starts with a TSH and free T4 in your blood.
I often see these complaints dismissed as a busy life or ageing, while a simple blood value can give the answer.
What is a slow thyroid?
With a slow thyroid your gland makes too little hormone, so your metabolism slows. Your pituitary tries to compensate by making more TSH, which you see back in your blood. The pace of your whole body drops a notch as a result.
The most common cause is an autoimmune reaction, in which your defence slowly damages your thyroid. That process runs creeping, which explains why the complaints often stand out only late.
What are the symptoms?
The complaints develop slowly and are vague, so they stay unnoticed for a long time. A review in The Lancet names fatigue, cold intolerance, weight gain, constipation and dry skin as common symptoms (Chaker, 2017).
- Persistent fatigue and low energy
- Feeling cold, especially in hands and feet
- Weight gain without a clear reason
- Dry skin and hair loss
- Low mood and slow thinking
None of these complaints proves a slow thyroid on its own. Only a blood value completes the picture.
Which blood values are involved?
The work-up starts with TSH, supplemented with free T4 if it deviates. With a slow thyroid you usually see a high TSH with a low or low-normal free T4.
| Value | With a slow thyroid |
|---|---|
| TSH | Often raised |
| Free T4 | Low or low-normal |
| Anti-TPO | Raised with an autoimmune cause |
This article belongs to our guide your thyroid and metabolism. The TSH value itself we cover in TSH levels explained.
Slow thyroid, training and weight
Because your metabolism slows, a slow thyroid can hold back your recovery and make weight loss harder. If you train hard without result and feel flat, a thyroid test is a logical check. If you feel tired despite good training, read tired despite training.
At the same time the thyroid is rarely the only factor. Look at your value alongside your broader hormone and metabolic status.
What do you do about it?
A proven slow thyroid is treated by a doctor, usually with thyroid hormone. According to Thuisarts, after the diagnosis a treatment follows along with monitoring of your values over time.
Compose your own panel through our custom blood test, or choose the general hormones blood test. A deviating value you always discuss with your doctor.
Subclinical hypothyroidism: the grey area
Sometimes your TSH is slightly raised while your free T4 is still normal. That is called subclinical hypothyroidism, and it is a grey area that doctors handle differently. Not everyone with these values has complaints or needs treatment.
An extensive review describes that subclinical thyroid abnormalities can have effects on your heart and bones over time, but that the approach differs per person (Biondi, 2008). Whether treatment is useful depends on your values, your age and your complaints.
In this grey area in particular a repeat measurement is valuable. A one-off slightly raised TSH can recover on its own, while a lasting rise means more.
Leave the interpretation of this to your doctor, who weighs your whole picture. Adjusting with medication yourself is not wise here.
References
- Chaker L, Bianco AC, Jonklaas J, Peeters RP. Hypothyroidism. The Lancet. 2017;390(10101):1550-1562. PMID: 28336049.
- Biondi B, Cooper DS. The clinical significance of subclinical thyroid dysfunction. Endocrine Reviews. 2008;29(1):76-131. PMID: 17991805.
- Thuisarts.nl / NHG. Thyroid disorders. Accessed 2026.
Disclaimer
Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. A blood test is a tool to walk into the conversation with your GP better informed, not a diagnosis in itself. For treatment decisions, discuss your results with your GP.
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