Take potassium iodide for thyroid-stimulating hormone. This is the one to buy.

Potassium Iodide is the strongest evidence signal for this outcome.

• Potassium IodideThe pick

  Strong evidence · 330 mcg (calculated)

  Inorganic iodine salt used to fortify salt and supply the thyroid; rapidly absorbed, making it a reliable source for preventing iodine deficiency.

• Biotin

  Strong evidence · 43 mcg

  Vitamin B7 and cofactor for carboxylase enzymes in fat and amino acid metabolism; deficiency causes hair thinning and skin rash.

• D-Biotin

  Strong evidence · 45 mcg

  The biologically active, naturally occurring stereoisomer of biotin (vitamin B7); supports fatty acid synthesis, amino acid metabolism, and is the form used in virtually all supplements.

Potassium Iodide at 330 mcg (calculated) lands inside the studied 150-500 mcg window.

Strong trust signals — consistently high marks from verified buyer ratings. Each product gets a DoseRank score blending clinical strength, evidence, dose fit, trust and value. Retailer links may be affiliate links — the scoring model decides placement, never payment from a brand.

$0.09 per serving — low price tier for this outcome. The cheapest ranked pick here is $0.01 per serving.

• 3
  Natural Factors, Liquid Kelp, 1.6 fl oz (50 ml)Score 87 · $0.01/serving
  iHerb
• 2
  Life-flo, Liquid Iodine Plus with Potassium Iodide, Unflavored, 2 fl oz (59 ml)Score 87 · $0.02/serving
  iHerb

Why not the absolute cheapest? The DoseRank score also weighs clinical strength, evidence, dose fit and trust — the very cheapest listings rarely hold up everywhere else.