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# Human Radiolabeled Mass Balance Study Guide
- URL: https://www.fdaweb.com/human-radiolabeled-mass-balance-study-guide/
- Published: 2024-07-18T12:00:00.000Z
- Updated: 2026-09-14T14:35:49.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5157380

FDA has published a guidance, *Clinical Pharmacology Considerations for Human Radiolabeled Mass Balance Studies*, with agency recommendations for such studies in investigational drugs, including **(1)** deciding whether and when to conduct the study, **(2)** designing the study, and **(3)** reporting results. The [document](https://www.fda.gov/media/158178/download?ref=fdaweb.com)’s recommendations are based, in part, on the agency’s experience reviewing human radiolabeled mass balance studies submitted in recent NDAs, FDA says. The guidance does not cover animal mass balance studies, safety testing of drug metabolites, or recommendations for selecting the radioactivity dose.