Potassium Iodide Side Effects: What to Know Before Taking KI

When taken as directed during a radiation emergency, potassium iodide is generally well tolerated. However, like any medication, it can cause side effects ranging from mild discomfort to rare but serious reactions.

Common (Mild) Side Effects

Metallic or brassy taste in mouth
Burning or tingling in mouth and throat
Sore teeth and gums
Runny nose, increased saliva
Gastrointestinal upset: nausea, vomiting, diarrhea, stomach pain
Headache

Serious Side Effects (Seek Emergency Care)

Fever, joint pain
Swelling of face, lips, tongue, or throat (angioedema)
Difficulty breathing or swallowing
Severe skin rash, hives
"Iodide mumps" — swelling of salivary glands

Contraindications

Dermatitis herpetiformis (Duhring's disease)
Hypocomplementemic vasculitis
Nodular thyroid disease with heart disease (risk of thyrotoxicosis)

Drug Interactions

Dangerous Interactions

ACE inhibitors + potassium-sparing diuretics: Combined with KI, these can cause dangerously elevated blood potassium (hyperkalemia). Antithyroid medications (methimazole, propylthiouracil): KI plus these drugs can cause excessive thyroid suppression.

Special Populations

Neonates: Repeat dosing risks transient hypothyroidism, which can affect brain development if unmonitored
Adults over 40: Higher risk of KI-induced thyroid dysfunction
Pregnant women: Safe at recommended dose but monitor for neonatal thyroid effects

Seafood Allergy?

Per the FDA, seafood allergy is NOT a contraindication to taking potassium iodide. Seafood allergies are caused by proteins in seafood, not by iodine.