Underactive Thyroid: Separating Myth From Guidance
Underactive Thyroid: what people commonly get wrong, set against what published US guidance says.
Symptoms are vague and easily put down to aging, stress or low mood, and treatment is usually a single inexpensive daily pill.
Key takeaways
- Main test: TSH, with free T4 if abnormal
- Pattern: high TSH with low T4
- Most useful single change: Take levothyroxine on an empty stomach at the same time every day.
- Commonest mistake: Taking it with breakfast, coffee or supplements.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
What the guidance actually says
The published position, before we get to what people believe instead.
| Measure | Figure |
|---|---|
| Main test | TSH, with free T4 if abnormal |
| Pattern | high TSH with low T4 |
| Treatment | levothyroxine, usually taken daily for life |
| How to take it | on an empty stomach, 30-60 minutes before breakfast |
| Retest after a dose change | usually 6-8 weeks |
Where people go wrong
These are widely believed and not supported by the guidance above.
- Taking it with breakfast, coffee or supplements
- Adjusting the dose yourself
- Buying thyroid products online, including unregulated thyroid extracts
What to do instead
- Take levothyroxine on an empty stomach at the same time every day
- Separate it by about four hours from iron, calcium and antacids
- Have TSH rechecked 6-8 weeks after any dose change
- Tell your doctor as soon as you become pregnant; the dose usually needs increasing promptly
The part that is genuinely uncertain
Guidance changes, and it changes because evidence does. The figures above reflect current US guidance from the bodies named at the foot of this page; where those bodies revise their position, theirs is the account to follow rather than this one.
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- What the Guidance Really Says About Fatigue in Long-Term Illness (Long-Term Conditions)
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Where to go next
- Your Questions About Underactive Thyroid, Answered
- Underactive Thyroid at a Glance
- Underactive Thyroid — the reference entry
- Thyroid and Hormones: The Complete Guide
- Overactive Thyroid: Sorting the Evidence From the Noise
- What the Guidance Really Says About Thyroid Function Tests
When to speak to a doctor
Contact your doctor promptly if you become pregnant while taking levothyroxine, and report palpitations, tremor or weight loss, which can indicate too high a dose. Call 911 for extreme drowsiness, confusion, very low body temperature or collapse, which can indicate severe untreated hypothyroidism.
Where this comes from
- American Thyroid Association — Hypothyroidism (Underactive)
- National Institute of Diabetes and Digestive and Kidney Diseases — Hypothyroidism (Underactive Thyroid)
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.
Spotted something wrong? Report an error on this page. We correct on the page and say what changed.
