What is the difference between mg and mcg for peptides?
mg means milligrams. mcg means micrograms. One mg equals 1,000 mcg. Peptide vials are usually labeled in mg because that is the total powder in the vial. Individual doses are often entered in mcg because they are much smaller.
The conversion
- 1 mg = 1,000 mcg.
- 0.5 mg = 500 mcg.
- 0.25 mg = 250 mcg.
- 2 mg = 2,000 mcg.
Why this matters
If you enter 2 mg when you meant 200 mcg, you entered ten times more than intended. If you enter 250 mg when you meant 250 mcg, the math becomes impossible because the dose is larger than the vial.
Rule of thumb
Use mg for the vial label and mcg for the target dose unless the specific compound page clearly uses mg-scale dosing.
Pepdex is an educational reference, not medical advice. Peptides vary in legal, approval, and evidence status. This answer is meant to explain the concept, not prescribe a protocol or replace a qualified clinician.
Helpful next pages
More dose math answers
Last updated 2026-07-07.