mg vs mcg dosing

Why does mixing up mg and mcg matter?

NIST's metric-prefix table defines milli as one-thousandth (10⁻³) and micro as one-millionth (10⁻⁶) [1]. That makes one milligram equal 1,000 micrograms. Mistaking one unit for the other is not a small rounding error — it shifts a dose by three orders of magnitude, and unapproved product labels are not always written the same way as approved ones.

How do approved drug labels state strength?

Mounjaro's label states each single-dose pen or vial contains a 0.5 mL solution of 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg or 15 mg of tirzepatide [2]. That is how an FDA-approved peptide drug states its strength: a specific mass, per a specific volume, on a label FDA has reviewed. Products without FDA approval have no equivalent label FDA has checked for accuracy.

How has unit confusion gone wrong?

A pediatric case report describes a 5-year-old who weighed 17.5 kg receiving 50 mg of clonidine after "a pharmacy compounding error in which milligrams were substituted for micrograms" — its title calls it "A 1000-fold overdose" [3]. FDA's Semax briefing separately records vendor-nominated strengths of "7,500 µg/mL or 1,000 µg/mL" for a product with no FDA-approved label [4], an example of the microgram-level labeling unapproved peptides use without FDA review.