Some new medical writers interested in regulatory writing ask about the difference between NDAs and INDs. In simple terms, when a drug is determined to be safe and effective, the manufacturer files a New Drug Application (NDA) with the FDA at completion of the clinical trials.
However, before the drug is approved, it has to be tested and shipped to other investigators. But how can the researchers use a drug not yet approved by the FDA? The answer is the Investigational Drug Application (IND), which allows an unapproved drug to be used in certain circumstances (there are different types of INDs, depending on the need).