Medication · antithyroid

Supplements and Propylthiouracil.

Every documented pair, every citation. Below: 3 documented pairs grouped by mechanism.

Propylthiouracil is an antithyroid agent used in hyperthyroidism.

Propylthiouracil is an antithyroid agent used in hyperthyroidism, typically Graves disease. UK endocrinology prescribes mostly carbimazole, or in pregnancy and certain other contexts propylthiouracil. Mechanism is interference with thyroid hormone synthesis at the level of thyroid peroxidase. The supplement surface is small because antithyroid drugs have minimal CYP metabolism. But two points sit at the centre. Iodine status matters. High iodine intake from kelp or iodine supplements opposes the antithyroid drug effect and is contraindicated. Selenium has been studied in Graves disease with modest evidence of benefit for orbital signs. The UK endocrinology consensus is that patients deficient in selenium may benefit, but routine selenium at high doses for everyone on antithyroid medicine is not supported. Carbimazole carries a small agranulocytosis signal that warrants prompt review of any unexplained fever or sore throat. Supplement choices do not change this monitoring.

Below are the 3 documented pairs we have explicitly assessed against Propylthiouracil in the Distil database: 3 amber. The pairs cluster around 1 mechanism: Antithyroid drug interference. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not on this list is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by supplement, and the missing-item form at the bottom of the page routes any uncatalogued supplement into our next curation pass.

Documented interactions

Antithyroid drug interference

Amber Bacopa Monnieri

Propylthiouracil works by lowering an overactive thyroid. Bacopa may gently raise thyroid hormone, so in theory it could pull in the opposite direction and make propylthiouracil a little less effective. This is based on animal studies rather than people, so it is a sensible caution rather than a firm warning. If you take propylthiouracil, mention bacopa to the clinician who manages your thyroid and keep to your usual thyroid blood tests.

PMID 12065164 · BNF: Propylthiouracil

Reviewer-flagged: awaiting clinical-reviewer sign-off.

Amber Iodine

Propylthiouracil is used to calm an overactive thyroid. Taking an iodine supplement at the same time can work against it by giving the thyroid more raw material to make hormone, which may make your overactive thyroid harder to control. Iodine supplements are generally not advised while you are being treated for an overactive thyroid unless a specialist has told you otherwise.

PMID 12213665 · PMID 36740774 · BNF: Propylthiouracil

Amber L-Tyrosine

Propylthiouracil works by lowering an overactive thyroid. L-tyrosine is a building block of thyroid hormone and at high doses can nudge thyroid activity up, so in theory it could pull against propylthiouracil and make it a little less effective. This has not been tested in people on propylthiouracil, so it is a caution rather than a firm warning. If you take propylthiouracil, mention L-tyrosine to the clinician who manages your thyroid and keep to your usual thyroid blood tests.

PMID 18274206 · BNF: Propylthiouracil

Reviewer-flagged: awaiting clinical-reviewer sign-off.

What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope (food-supplement interactions only; for drug-drug interactions, the BNF is authoritative). Use the checker below to surface any supplement, and submit a missing item if you take something we have not catalogued.

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For adults over 18. This tool gives evidence-graded information, not medical advice. Always discuss changes with your GP, especially if you take any medication, are pregnant, breastfeeding, or have a serious health condition.

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