Potassium iodide

What it is

Potassium iodide supplies iodine, the raw material the thyroid gland incorporates into its hormones. Without enough dietary iodine the gland cannot make sufficient thyroid hormone and may enlarge. It is available without prescription and is used to correct or prevent iodine deficiency and the hypothyroidism and goitre that can follow it, and it is a routine supplement in pregnancy in regions with poor iodine intake.

A usual adult range, not a national label — the dose and the timing differ by country and by product.

Used for

• Deficiency
• Hypothyroidism

Approved uses differ by country — some of these may be off-label or unapproved where you live.

What to know while taking it

It is taken with food and is usually well tolerated. Iodine is not simply a tonic for the thyroid: in an already diseased gland, extra iodine can tip function in either direction, unmasking overactivity in a nodular goitre or worsening underactivity in autoimmune thyroiditis, which is the reason for the caution note. TSH and free T4 show which way the gland is moving and are the sensible way to judge whether supplementation is helping.

When to see a doctor

Palpitations, tremor, unexplained weight loss, heat intolerance, or a visibly growing or tender neck swelling mean see a doctor. So does a metallic taste, burning in the mouth or throat, or a rash, which can signal iodine sensitivity.

Worth knowing

• Caution with thyroid disease

Markers to watch

• TSH
• Free T4