Propylthiouracil (Antithyroid)

Propylthiouracil (PTU) is a metabolic drug. This page provides educational reference information about Propylthiouracil and focuses on what else you may be taking that could interact with it, including medicines and supplements such as Ashwagandha, Vitamin B7 (Biotin), Sea Moss (Irish Moss), Holy Basil (Tulsi), and Iodine.

For questions involving a medical condition or combining products, consult a clinician.

The most important concerns involve combinations that can make thyroid control less predictable. Ashwagandha may increase thyroid hormone activity, while the iodine content of Sea Moss (Irish Moss) may oppose propylthiouracil’s therapeutic action. These combinations could contribute to recurrent hyperthyroid symptoms and warrant review with a prescriber or pharmacist.

Holy Basil (Tulsi) may add antithyroid activity to propylthiouracil, potentially pushing thyroid activity too low; this concern is based on preclinical evidence and is not established in the same way as a well-documented clinical interaction. Vitamin B7 (Biotin) presents a different issue: it can distort results from susceptible thyroid laboratory assays, which may lead to inappropriate treatment decisions or dose escalation and subsequent iatrogenic hypothyroidism. Anyone using biotin should make sure the clinician interpreting thyroid tests knows about it.

Iodine can also have a specific supervised role rather than being uniformly incompatible with propylthiouracil. In thyroid storm, pharmacologic iodide is administered after propylthiouracil to inhibit hormone release while propylthiouracil blocks hormone synthesis and peripheral T4-to-T3 conversion. This is a clinical treatment context and should not be treated as guidance for self-directed iodine use. Pharmacology references support reviewing these combinations with a healthcare professional, particularly when thyroid symptoms or laboratory results change.