Baby Safety / Compounds / Propylthiouracil (PTU)

Is Propylthiouracil (PTU) safe for babies and kids?

Very high risk for kids

Transferred via breast milk. Neonatal thyroid monitoring required.

What is propylthiouracil (ptu)?

CAS number
51-52-5
Molecular formula
C7H10N2OS
Molecular weight
170.23 g/mol
SMILES
CCCC1=CC(=O)NC(=S)N1
PubChem CID
657298

Risk for babies

Very high risk

Transferred via breast milk. Neonatal thyroid monitoring required.

Risk for pregnant and nursing people

Very high risk

Crosses placenta. Can cause fetal goiter and hypothyroidism. Associated with aplasia cutis. Preferred over methimazole only in 1st trimester.

Regulatory consensus

2 regulatory and scientific bodies have classified Propylthiouracil (PTU). The classifications differ — that's the data.

AgencyYearClassificationNotes
FDA1947Approved drug — restricted to 1st trimester pregnancy (black box: hepatotoxicity)
OECD2009Reference thyroid disruptor for OECD TG 231 (amphibian metamorphosis assay)

Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.

Where kids encounter propylthiouracil (ptu)

  • Pharmaceutical
  • Environmental Contaminant

Safer alternatives

Lower-risk approaches that achieve a similar outcome to Propylthiouracil (PTU):

  • Methimazole (preferred outside 1st trimester)
    Trade-offs: Alternative approach; specific tradeoffs depend on application context, scale, and regulatory requirements. Full hazard assessment of alternative recommended before adoption to avoid regrettable substitution.
    Relative cost: 1.2-2×
  • Radioiodine ablation
    Trade-offs: Alternative approach; specific tradeoffs depend on application context, scale, and regulatory requirements. Full hazard assessment of alternative recommended before adoption to avoid regrettable substitution.
    Relative cost: 1.2-2×

Frequently asked questions

Is propylthiouracil (ptu) safe for kids?

Transferred via breast milk. Neonatal thyroid monitoring required.

See Propylthiouracil (PTU) in the baby app

Look up products containing propylthiouracil (ptu), compare to alternatives, and explore the full data record.

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Sources (1)
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Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →