Oxymetazoline Base (CAS No. 1491-59-4) in bulk powder form. Oxymetazoline is a vasoconstrictor indicated for the topical treatment of persistent facial erythema associated with rosacea in adults. It is also used for the temporary relief of nasal congestion caused by allergies or the common cold. In your letter, you stated Oxymetazoline Base is being studied for the treatment of rosacea.
[1] Please importantly note that only the relevant portion of the related is displayed above. You may refer to the said customs ruling for the entire ruling explanation.
[1]. https://rulings.cbp.gov/ruling/N321273