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# MUsT Guidance Helps OTC Studies
- URL: https://www.fdaweb.com/must-guidance-helps-otc-studies/
- Published: 2018-05-23T12:00:00.000Z
- Updated: 2026-09-15T00:07:32.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5141513

CDER director of nonprescription drug products **Theresa Michele** says that a new draft [guidance](https://www.fdaweb.com/maximal-usage-trial-draft-guidance/) on maximal usage trials (MUsT studies) will help industry design and conduct MUsT studies for topical active ingredients that are under consideration for inclusion in an OTC monograph. Writing in an *FDA Voice* blog [post](https://blogs.fda.gov/fdavoice/index.php/2018/05/the-fda-issues-draft-guidance-about-the-absorption-of-active-ingredients-being-considered-for-inclusion-in-over-the-counter-drug-products-applied-to-the-skin-and-marketed-without-approved-applications/?utm%5Fcampaign=FDA%20Voice%20The%20FDA%20Issues%20Draft%20Guidance%20About%20the%20Absorption%20of%20Active%20Ingredients&utm%5Fmedium=email&utm%5Fsource=Eloqua), Michele says the agency has been encouraging manufacturers to collect data on the potential risks of a topical drug when used according to the maximum limits of the product’s instructions.

Such studies are important, she writes, so FDA and sponsors can better understand the absorption and safety profile of topical OTC products such as sunscreens and topical antiseptics. “We are particularly interested in learning how these products affect vulnerable populations such as children, the elderly, and pregnant and breastfeeding women,” she says.