How long does it take for tetracycline to stain your teeth?

During formation: Tetracycline staining occurs during formation of the teeth, before they actually erupt in the mouth.. Anytime from age birth to 12. It doesn't matter how long. What matters is if it is taken during the growth of the tooth. Taking it after the teeth are already in the mouth will not cause discoloration.

Intrinsic Staining: The antibiotic tetracycline gets incorporated into tooth structure that is forming. It does not stain the surface as does coffee, tea and red wine, for examples of extrinsic stains. From birth to about 15 years of age is the time to avoid giving tetracycline, unless no other antibiotic is available.