What is a bulk drug substance?
Short answer · as of 2026-10-05
For the compounding sections of the FD&C Act, FDA's regulation says bulk drug substance has the same meaning as active pharmaceutical ingredient. That is a substance intended for incorporation into a finished drug that furnishes pharmacological activity or another direct effect. It names the ingredient, not the finished product, and the term alone says nothing about whether an ingredient may be used in compounding.
By Peptide Industry Gossip · Published · General explanation, not legal or medical advice. Disclaimer.
What the regulations say
21 CFR 207.3 says that, as used in sections 503A(b)(1)(A) and 503B(a)(2) of the FD&C Act, bulk drug substance means the same thing as active pharmaceutical ingredient as defined in section 207.1.
Section 207.1 defines an active pharmaceutical ingredient as a substance intended for incorporation into a finished drug that furnishes pharmacological activity or another direct effect in diagnosis, cure, mitigation, treatment or prevention of disease, or affects the structure or function of the body. It excludes intermediates used in synthesis.
Why the term shows up
Both compounding routes turn on the ingredient. Which bulk substances a 503A pharmacy or a 503B outsourcing facility may use is governed by the lists and conditions explained on our compounding pages. The import alert for GLP-1 ingredients also uses the term in its title.
What the term does not say
- It does not say the substance is eligible for compounding. Eligibility is a separate question, answered by the bulks lists and statutory conditions.
- It does not say a finished product is approved. A compounded drug made from an approved ingredient is still not FDA-approved.
- It does not make a vial sold as a research chemical a drug ingredient. How a product is labeled and marketed is what FDA examines in its letters.
Sources
- Legal Information Institute, 21 CFR 207.3: definitions
- Legal Information Institute, 21 CFR 207.1: definitions